Originally posted by clockwork247 k-r is a midrange camera (even though it replaces the entry level K-X) D3100 is a pure entry level (nikon made sure of that, I'm not sure if it even has a built in focus motor).
I would never touch a nikon unless it's their high end range... i just feel they cheapen the entry level alot more than any other brand.
You are correct, the D3100 does not have a built-in focus motor so it will only work with the newer Nikon lens. I only have the 35mm f1.8 and the 18-105mm lens that I use and am fairly happy with them.
When I ordered the K-r, I was sure to get the 35mm f2.4 and have just ordered the 18-135mm so the setup should be similar to the D3100. I'm just a casual photographer, mostly taking pictures around the house and whatever event we are going to. My wife and I will be visiting the Titanic museum here in Indy tomorrow, so I'll be able to hopefully get some good pictures with the K-r.