Went to B&H yesterday and got the K-3 with battery grip and a DA* 300 f/4. Today I was able to go out for some shooting. Overall I'm very impressed. The files are so much sharper and more contrasty than what I ever got with my D7000. The AF performance feels very different from my nikon. Not bad, just has a different feel. In some ways it's definitely better. For example with the D7000, I would never use anything besides single point or nine point AF, anything else wasn't precise enough, whereas with the K-3, even using the full array of points gave me accurate focus where I wanted it. I still need more practice, but I was having trouble tracking some gulls in flight. They weren't being very cooperative in the first place, so I'll have to postpone my judgement for now. Here are two shots from today:
The ergonomics are great, as expected.