Off the top of my head, in terms of most improved I can think of a few:
1) Stricker
2) O'hair
3) Toms
For Stricker and O'hair, the big thing was they have confidence in there overall games and play in alot of big situations and had some pretty good success. Basically, they know they can perform well in the big moments now
For Toms, he returned to Cleveland, got healthy (I think he had some injury issues) and maybe got some great instruction (just guessing with this last one).
In terms of who has fallen the most, I would suggest Anthony Kim. Sure he had some success at the President's cup, but I didn't think he was near the player he was this year compared to 2008. I think injuries contributed to his downfall