Well i've had one of the original (metal case) DJM600s for over 6 years now and it is in perfect working order, even after the eq and fader abuse that techno normally takes its toll on mixers... i have never come across a mixer as robust as the DJM600.. I've seen Vestax and A&H pack up after a couple of years, noone i know with a DJM has ever had any problems with them..
I can't really comment on the CDJs but i think the DJMs are worth their weight in gold.