Similar design to D7000
While there are a few control layout changes -- some of which I like, others of which I don't -- overall the D7100 has the same look and feel as the D7000. However, the new model is of sturdier construction; it's composed of magnesium alloy and weather-sealed much like the D300s.
There are four major changes here. Yay for the lock button on the mode dial, though I don't like it in the center. And there's now a built-in stereo microphone. Plus, Nikon's replaced the annoying dangly strap mounts with fixed rotating ones. But the movie record button is one of those too-small, poorly placed controls that's unfortunately become quite popular.
The grip on the D7100 is noticeably deeper -- even though the body itself is the same depth -- and feels a little more comfortable.
Here you can see the more curved shape of the grip, which adds to its increased comfort. The camera retains the dual SD card slots.
That rubberized portion down the right side is also new, an expansion of the thumb grip from the D7000.
The real changes are on the back. The lock button is now integrated with the navigation control -- which I like -- but the record button has been moved to the top, where I don't like it. I liked the Live View toggle switch on the D7000, but the D7100 uses a more typical control. The i button on the bottom left is new and adds quick-menu functionality.