What I do like so far over my K10D:
Faster focus, even with the SDM lens
Seemly better exposure
Better dynamic range (was shooting swans earlier and I found it easier to get the details in their feathers)
Fast FPS is great for catching ducks landing on the water. Too bad they only did it when I wasn't looking
Quiet shutter. All the ducks/swans swam away from the guy with the big Canon over to me, maybe his shutter was too loud
Ergonomically the size sucks and I don't like that I have to press and hold the OK button to switch between AF point selection and WB, etc... but I suppose that's the tradeoff for a lighter body.