I know several people that can't readily hear a difference between 16 and 24-bit. But if you can't hear a difference between 16 and 8 bit, you should probably have your hearing checked (seriously).
Explanation? Word length (and therefore, dynamic resolution) of the bounce. 8-bit, 16-bit or 24-bit. 24-bit is a "standard" (for lack of a better term) resolution for pretty much everything up to the final delivery format where it might be changed to 16-bit (for CD-A) or what not.