I agree with Dave, but I think a producer can have "his" certain sound and still not be repetitive... Some artists that have been mentioned above have all had their share of samey releases, but on the other hand, there are artists, whose sound is identifiable by ear (by that I mean the production), but still manage to surprise (and amaze) with every new release... The Kanzleramt cats or the french techno scene (people like The Youngsters and/or Southsoniks) have that certain something, as do some other producers... OK, I guess some people will argue that every new Ben Sims release is totally different, but the point is you don't need to sell your "sound" like a formula, making all your releases formulaic... Because it stops being art when you're stuck with a blueprint and you just twiddle around with a few parameters to make it different ;)