I'm liking the whole Greatest Deeds tracking thing.  Here's a thought I had that sounded kind of fun.

Cut up the Greatest Deeds sheet into 8 individual "cards".  Award the cards to whoever the current record holder is.  A card can be "spent" for a free point of Divine Favor at which point it is returned to the GM until someone sets a new record and is awarded the card again.  If the record is broken before the card is spent...tough, hand it over to the new owner.  Whoever has the most cards in their possession when a quest ends earns a new Divine Favor Box in addition to the "completing a quest" box.

I was thinking about making it a free point of Divine Favor or Fate, but that might muck with the Fate economy.

Awesome. I love it.

But don't mess around with Fate. It should never, ever go down. Unless you meant up? In that case... interesting.

I like this.
I'm a bit unsure about the adding divine favour to the guy who has most cards - as I see it, divine favour is going to be going up rapidly enough already, plus once you have a couple of those cards in your possession, it might be harder to remove them. Some (like Highest Roll) might tend to 'stick' to a character for a long time, so this +1 Divine Favour might be gained repeatedly by a single character.

Also, what about the other 8 boxes: the blank boxes. Once a mechanical reward is associated with the cards, you might need some way of figuring out how to create those extra categories - if they are used.

But those are just minor worries that may amount to nothing. What do you think?

Hmmm.  Honestly, my main thought with Greatest Deeds was to give them a point value that added into the character's Legend total.

I don't think I'd want to mess with the Legend track. (Especially since you have to add the point value, then later remove it when someone eclipses your benefit - a bit fiddly).
I like the Greatest deeds being separate from Legend. Your Legend shows how famous and legendary you are, the Greatest Deeds show some of the things that are talked about when your name is mentioned.

Ralph's suggestion (one divine favour, once per award) is actually a very minor award. You can easily blow through 7+ divine favour in a battle (even in a single action).
The way I think I'd now run it: for each greatest deed you have, you get given a card at the start of the session. You can hand the card in for 1 divine favour, and you get the card back at the start of the next session.

Or:
A card can be handed in for any Divine Favour benefit, regardless of cost. Once used, it is gone until that greatest deed is eclipsed and the card is awarded again.
Or, maybe, a card can be used to add a +2 bonus, but only to actions that fit the card. (So the highest ability roll could be used for anything, but the Most Minions card would only be used when fighting Minions.) Actually, I like this idea a lot. Though it does have the danger of slightly reinforcing a person's owenership of the card. But I think the bonus is infrequent enough that the danger of that is slim.

I like the idea of having the cards in play, in front of their owners, a constant reminder of who has those awards - a constant encouragement to otehrs to try to get them. If the card is used up when you use it just once, part of that benefit is lost.