I have had a Klien Attitude Comp disk 2003 for about a year and I'm not impressed.
Everything is there but no thought has gone in to how to make it all work together. There seems to be some flaw in the frame design which put the chain too far out from the centre line. This meant the chain wouldn't stay on the two biggest cogs on the rear when it was on the middle front ring. The only way around this was to take a couple of mil off the bottom bracket on the chain side. More expense.
The thing often creaks when pedaling, to the point where I've thought the frame must be cracked somewhere. I can't find anything wrong, I just don't understand it. The shop I bought it from said it was cables (they run inside the top tube) and, for a not too small a charge, put a new one in for me. Made no difference.
The Hayes disk brakes are awful, well the front one is. I've never been able to get it to work properly and neither have the two bike shops I've given it to to look at. The one I bought it from and the one I went to when I gave up on them. At least they solved the gear thing rather than just saying it was inherent in the design and anyway, why would I want to use that gear combination? One of the front pistons was sticking and had to be replaced very soon after I bought it before I'd done anything challenging. It's still not right and even if it were, it appears that the whole caliper is slightly off centre. Sadly not the right way to compensate.
The tyres it comes with, Bontrager something or other, are terrible in all conditions I've tried them in.
I like the colour, though, but I would advise against buying a bike for this reason alone!
All in all you don't want to be spending lots of money rectifying problems that should never be there on a bike that costs this much. So my recommendation is stay well clear of Klein and be sure your dealer will give you proper support before you give them your money. I shan't be going back to Beyond Mountainbikes (in Cranleigh, Surrey UK) and I won't be buying Klein from anywhere again.
Good luck.