I have an '02 300 MXC that I picked up in July. Can't say that I'm totally thrilled with it but most of the "problems with the bike" are really "problems with me".
1. The MXC has a close-ratio transmission and, at least for my slow riding, is geared too high for the tight trails. If you lower the overall gearing, you lose a lot of top speed. For my "riding style" (if you can call it that), the EXC, with it's wide-ratio transmission, would have been a better choice. The EXC is also geared high for the tight trails (don't flame - IMO) but, with the wide-ratio transmission, you can lower the overall gearing and still keep good top speed.
2. I'm still futzing with the jetting on the darn thing. It ran very rich from the outset and I've been slowly working it down. I'm next going to try the 170 main (two notches leaner than stock) and see if that gets me there.
3. It's so darn tall! But then they all are and, yes, this is a personal problem.
4. It's so darn powerful! And, yes, this is also a personal problem. I would probably have been better off with a less powerful machine. At least while I'm still re-learning the sport.
5. The stock seat cover will need to be replaced (color fading and tearing problems?) but that is covered under KTM's warranty. Make sure your dealer does this for you at no charge.
6. I wish the forks allowed preload adjustment (has compression and rebound damping only). They're too stout for me so I need to look for a lighter spring.
End of griping.
The components are top-notch. You get stuff on a KTM that you'd have to get after-market on the jap bikes (suspension, hydraulic clutch, etc.).
Hope this helps.