So, I've tried to play D&D on a forum before and it went reasonably well...  Until we got into combat.  A single combat encounter (even an unimportant encounter) took about a week to get through before we could actually start role playing in interesting (as subjectively defined by me) ways again. 

The Shadow of Yesterday (and perhaps Narrativist games in general) seems like it would go well in a forum.

So, my questions are:
1.  Has anyone tried this before?  If so, how did it go?
2.  Would anyone else be interested in playing TSoY via forum? 

I think the Italians at Gente Che Gioca have played TSoY as a forum game. The same goes for Germans at Tanelorn, unless I misremember. I'm not very familiar with the form myself, though, so don't really know about the specifics. I might imagine that players well versed in the SS rules would manage to play through their "turns" with relevant fictive content in each contribution; this, I understand, is the main hindrance in forum play - it gets boring if the game in question needs a lot of trivial turns in between relevant play. SS combats in comparison to D&D combats might be a bit more bearable because of less whiffing and the necessity of positioning the characters anew for each individual combat round; interesting stuff happens in the fiction all through the events, in other words. And of course a situation would never go into detailed resolution without being interesting in the first place.

I could see myself trying out a forum game of TSoY at some point, I suppose. I'd probably make it a low-tech affair only for a couple of players - a single thread with no technical separation of IC vs. OCC communications. What little experience I have with the form has left me a bit cold on how forum games are usually arranged; lots of effort is put into separating mechanical discussion from the fictional account (separate threads, differing colors, etc.), which to me defeats the whole point of playing an organically mechanical game like TSoY in the first place.

But anyway, do let us know how it goes if you get to try it. I'd be interested in whether the mechanics cause a lot of empty spinning in practice, and if there are some subsystems that are better off dropped or modified in a correspondence game.

So, the first major issue I ran into was that I couldn't find a good, free piece of forum software that had the capability of rolling Fudge dice.

I decided to use Vanilla forums since they were open source and had some nice plugins and wrote my own dice-rolling plugin.  So, if anyone on The Forge wants to host their own forum with a dice roller, you can download vanilla at:  http://vanillaforums.org/ and my Dice Roller plugin at http://vanillaforums.org/addon/diceroller-plugin.

I'll probably make some modifications to it so it'll do some fancy TSoY stuff (like account for bonus, penalty, and overflow dice).

Also, it should be easy enough to customize the code so it works for other various games.

With the technology online, I can redirect my focus to the game.

As a point of clarification, my comment:

Also, it should be easy enough to customize the code so it works for other various games.