I went from the K20 to the K5 last week and I'm sure enjoying it as well. The high ISO is amazing. I now shoot at ISO3200 and don't even think about it. I had handled a K7 before in the store (it wasn't charged, though) so I knew what to expect size-wise. What really surprised me was the lack of shutter sound. My friend was looking at it (he just bought a D700) and he was snapping shots, and I couldn't even hear it. He kept looking at the LCD and I was wonder what he was looking at, when I saw that he was actually shooting.
I haven't read the manual yet. (That's just some guy's opinion, anyway.) However, some of the functions are taking me a while to figure out. I may have to break down and give it a read. I like the Live View implementation and AF. I won't use it that much, but it's nice to have. I haven't played with the video yet. I'll give it a try, though again, I probably won't use it that much.
All in all, I'm very happy, and it seems to be living up the the standards my K20 laid down, and then some.