I do not personally own one...but HAVE used one and can say its a fantastic camera for various reasons. Its a bit heavier than the D3100 but nothing that will make you uncomfortable. I say if you are looking for a really nice camera that won't break your bank..get it! Its not as fancy or well built as the D7000, but damn close.
I know that if I went with the Nikon 5100 I would be taking a step down from my current camera, but I never used my camera to it's fullest potential. I thought maybe I don't need THIS much camera yet. :ROFLOL:
I'm also thinking about getting one of these cameras. This will definitely be an upgrade for me and an introduction to the dslr world, but I am ready to take on the challenge of learning about this camera.