We recently upgraded our camera to the Nikon D5100 (body only). Our D40 has served us well but has started to show signs of trouble. We and many others were getting a shutter release error where you can't use the camera. Although people claim the WD40 trick works, we figured it was time. Usually a good whack does the trick but not always.
The new camera takes video and has a live monitor so you don't always have to look through the eye piece. It also has 11 auto focus areas which means it should focus a lot better than the D40's 3 areas. The megapixel's also increases from 6MP to 16MP. The high ISO performance works really well making it a lot easier to catch Lauren's and Cole's indoor soccer matches.