I've been putting some thought into how to make a list of skills as small as possible and still be some semblance of accurate. I'm lazy, and don't like book keeping when I play games, so games with minimal number tracking and/or small skill lists

So what is the smallest list of meta skills possible to cover ALL the activities one could hope to do in a game?

It's safe to say you will have large swath of skills be setting base (not many computers to hack in a typical DnD-esque dungeon) but there are still a host of skills common to all games.

These skills can further be looked at as being ones which are either common or uncommon and refined or advanced. It also occurs to me that most common skills are refine-able and most uncommon skills are advance-able. Also is seems that a bulk of these refine-able, common skills are physical in nature, while the uncommon and advance-able skills are more mental.

A good example would be Martial arts. People spend a life time devoted to it and, ideology on primal life force aside, never really learn anything new so much as refine what they already know and implement it more efficiently. Then look at any of the sciences, or trade crafts, or any number other professions. A person spending their entire life doing one of these often comes across new tools, methods, elements, and ways of thinking that are different from their prior experience and rather than refine what they've already learn, add to their knowledge.

There is some gray area in the above example. Most any conceivable trade skills can be focused on and refined, the craftsman producing work of higher quality and more quickly. Or a combatant spending time to wrap their head around the odd nature of some new exotic weapon, but it can still be viewed that the Physical execution of anything is largely refinement while the mental capacity for it is additive.

Not really certain if that effects anything but I think it's important to note.

From my point of view, all actions can fall into one or more of three groups. Physical, mental, or that mushy gray social intercourse. I've adopted this as my base for stats in at least one system, and I'm sure I'm not the only one. However they don't express clearly what is happening so more narrow ranges of skills must be derived. Since some skills can't be neatly tucked into anyone of these three, I'll refrain from using them. I'm approaching all meta skills as actions which can be learned by anyone. I will also try to explain why I believe it should be it's own skill.

Combat - fighting is potent cocktail of gross muscle movement, judgment, and self control unlike other highly physical activities such as sports.
Athletics- Raw physical ability focused through proper technique.
Diplomacy- Through words, expressions and body language be able to read and express meaning from and to others.
Artistry- The production of an element meant to influence individuals through their senses.

The above are all I could think of for Common meta skills. Everything else seems to be uncommon.
It becomes a tangled mess at this point, with some skills being very similar to others (the wide spectrum of medical professions), to moderately similar (Most fabrication trades) to highly specialized and not well related to anything (being  Scribe, or piloting a ship). Then there are the various Knowledges someone could have. History, Science, Magic, Religion, etc. These knowledges do not impart the ability to perform any task, though performing a task does not mean you have a strong grasp of the rules governing why you do what you do. There were blacksmiths and bricklayers long before there were material scientist and architects.

I'll attempt to group these skills as best I can anyways.

In my opinion, fallout 1 and 2, although CRPGs, have the best character generation system I've ever seen.  Add the piloting skill from tactics (which could be altered to horseriding to suit different genres) and the skill set looks pretty complete without being intimidating.  Fallout is my standard for measuring system elegance.

HM,
  This is one of my passions, and I have a procedure that works pretty good:
1) I list the conflict arenas that I want the game to support (physical, mental, social, spiritual, what have you)
2) I list the general types of activities that the game is about (fighting, survival, professions, etc.)
3) I put a skill in each intersection
4) I make sure that there is a catch all skill for each conflict arena (lore/education for mental, athletics for physical, etc.)
5) I make sure that each of the skills has a similar scope (meaning it applies to a similar number of situations, like Missile Weapons vs. Left-Handed Daggers)
6) Make sure that each stat (If my game uses them and the stats interact with skills) has a combat ability, a social ability, etc. So that any character can accomplish something in any conflict type, if they buy the right combo of skills and stats.
7) I make sure that each skill is meaningful, unique and symbolic (e.g., Artisan vs. Craft, each one says something different about your game, no?)
8) Playtest, this is the only way to be sure.
I hope that helps. I have examples if you need them.

3:16 has non fighting ability and...that's it for skills.

Skills, as in the actual written rules, are about managing gameplay/offering oportunity for playing input/managing player input and it's flow - they aren't about the fiction/the skills they are named after. Your idea of physical, mental and social groups is you trying to treat the fiction as if it has a ruleset/structure in it already.

MicroLite20 only has 4.
Physical
Subterfuge
Knowledge
Communication

I see that I made myself unclear. When i said that some skills don't fit into one of those three groupings (physical, mental, social) and they should be done away with, i meant the groupings, not the skill. The groupings can't accurately convey all skills, so they shouldn't be used.

What I want to look at is the nature of skills in  a game so that any action can be viewed and placed into a skill group, do to similarities it shares with other skills. In Fallout you have two skills 'Lock picking' and 'Repair' that arguably are similar enough as to be a single skill, as they both deal with the workings of simple mechanical devices. Some games like the later versions of D&D would combine them into 'Disable device'.
The opposite end of the spectrum is something like 3:16 or microlite20. Having a 'Non Combat' skill is so vague as to be all powerful. The context of the rest of the game keeps it in check, since the overwhelming focus of 3:16 appears to be alien blasting, but such a system in a more story oriented game would be unworkable. Microlite20 is better, as it starts to break up skills into more logical groupings, but the expansions cover new skill groups since the original 4 can't neatly describe everything that a character may want to do.

Why is there no edit button?

Anyways, I've thought more of the 4 groupings presented in Microlite20. It seems that the skills would work well for any setting except with special knowledges. Skills that require special knowledge are often setting specific, and of little concern in most gaming situations. You could there for have a set of 'common' skills which everyone would have, and 'Uncommon' skills that would be something unique only to a character who has taken it. I believe a listing of-
Combat
Physical
Subterfuge
Communication
Survival (here survival serves as a catch all to the basic roots of more advanced skills. think first aid and making simple tools)
(SPECIAL)

Having a 'Knowledge' or 'Academics' could arguably be on the list as well, but it is more ambiguous than the other skills. When does something go from being common to being specific knowledge? As a GM I would be more inclined to give info to players based on character backgrounds than anything else, letting a character with Special Skill - History being able to spout knowledge on some long dead civilization or the like.

I believe that many a game of various depth and play styles could be run with such a small skill listing, as games have already been shown to run on less.

I am working on a system with a set of 8 skills (although two can be made into multiple depending on the setting) and 8 attributes
The skills cover a large area, and combine with an attribute based on task.

Attribtues
Strength (Str) Presence (Pre)
Constitution (Con) Willpower (Will)
Dexterity (Dex) Intelligence (Int)
Agility (Agi) Perception (Per)

Skills
Artifice, Athletics, Combat,  Healing, Social. Stealth, Wrangle, Environment

So for swinging a sword you use Combat + Dexterity, for dodging that sword you use Combat + Agility, planning tactics is Combat + Intelligence, not being afraid of combat is Combat + Willpower

Environment is a catchall skill.  It is used for knowledge, piloting, etc in a particular environment.  So in a modern game you could have "streetwise".  When you want to find your way through a city it is Streetwise + Intelligence, when you want to spot someone in a crowd it is Streetwise + Perception, when you need to resist a cold virus it is Streetwise + Constitution.  Driving would be streetwise + dexterity.

The skills pretty much cover everything.  Presence does not divide into intimidation vs charm which I am sad about.

This thread is pretty similar to another I just commented on (skill block thread)

What do you think about defining a character in terms of background rather than skills?

my example was  Nobleman (3)  freebooter (1)  Pirate (5)  where the number represents proficiency/time in that area. 

You could also apply the same rationale to 'attributes'  which could give a bump on various rolls.  Nimble,  Tough, Strong, Charismatic, Sexy, Volatile, etc...

This character, for instance, could do anything 'piratey' with a proficiency of 5, and get a bump (+1) if the task at hand was helped in any way by being Charismatic, for instance.

Stefold, I love the idea. It gets players engaged in the world in a simple, elegant fashion. I'm trying to figure out how it would work within the heartbreaker I'm putting together... I'll mess around with it for a while and get back to you on how it works in action.

as a note - we played a call of cthulhu game with such a system (mountains of madness, so we were in antarctica)

my character had archaeologist 4, arctic explorer 3, and a couple of others.

it worked great for a horror game as we wanted light rules.  Having our abilities vague but comprehensive was nice.  We couldn't compare ourselves to our foes, or know just how tough things would be.  But then we also did not try to do something and discover we had left out that skill.

It made for a very fluid game.