K2 makes good bikes. The Disco Monkey compaired favorably with the Specialized Enduro a while back in one of the MTB mags. It's a bit on the heavy side for XC racing, but a VERY GOOD overall trailbike.
If you have the opportunity, you should demo one to ensure the geometry (top tube length, standover height, etc.) are suitable for you.
I have a '99 K2 Proflex 4000 that I got, new, in May '00. I love it! Really light, great suspension, x/c bike. Mine has the Noleen Crosslink front end, with the "smart shock". I think the smart shock is a pretty useless gimmick. It rides the same with it on or off. But the Crosslinks are sweet.
I added riser bars, and left everything else stock.