Well, the most obvious one is 24mp vs 16mp. This is a real difference but can only be realized with the best glass. I doubt the 18-105, that is pretty much standard issue, can take advantage of the mp differences. However primes like the 35mm 1.8, 50mm 1.8 80mm 1.8 and macro lenses should show you a real difference. The other differences are in the number of focus points and some other minor improvements. I have the D7000 and love it and I don't think the D7100 is enough of an upgrade for me to jump however, if I didn't already have a D7000, I would go for the D7100. (jmho)
All right! Lets say i shoot 12bit RAW and get the D7100.2-bits.
You will not be able to see any difference between a 12-bit Raw and a 14-bit Raw.
Another thing about the D7100 that is bugging me! Its the file sizes! I want to know how large the files are as it may eat up space on my SD Card and computer! How large are the File sizes? I would like to know the RAW file sizes. How large are they?