As a happy Nikon D7000 owner for more than two years, I immediately upgraded to the Nikon D7100. Rather than rehash all of the camera specs in this review, I'll focus on what has changed vis-a-vis the previous camera.
NEW 24.1 MEGAPIXEL SENSOR, 1.3x CROP MODE, NO AA FILTER
Although I didn't really care about having more megapixels, there are advantages. The most obvious is cropping and the NEW 1.3x CROP MODE is a nice feature if you are into bird & wildlife photography. This in camera crop converts lens focal length into 1.95 times the 35mm equivalent. (Usually DX cams have a 1.5x crop - this mode delivers and additional 1.3x.) So a 300mm lens that would normally perform as a 450mm on a DX (APS-C sensor) body now performs as a 585mm.