Nec: So far so good, I had a mk1 800 and I definitely prefer the feel of the mk2's jog dial (its supposed to be in line with the 1000 now but i've never used one so couldn't really say). Haven't used any mp3s with them yet which I guess is the main feature setting them apart from the mk1's, i'll have to burn some mp3's soon. Other than that, no major changes from mk1 but the little things (new display etc.) just make it a nicer deck to use.
DJ Elf: No massive changes, the main ones being mp3 playback functionality, jog dial changes (metioned above), improved display and bigger internal memory (I think its 10 cue points per cd now).