I'm part of a desert team that campaigns Husabergs. We've got a 400, 470, 501 and a couple of 650's in the stable. They are incredible bikes, but not for someone who doesn't like to work on bikes.
They are, essentially, factory race bikes and require about as much care and maintenance between rides. That said, they are incredibly simple and 'clean' when you look at them - there is no superfluous stuff on 'em, just what's needed.
The only mechanical issues we've had were cam followers and bearings (650's and the 400). The shifter on the 501 jammed in 4th during a night race a few weeks back, but was easily repaired in the shop afterwards. Jetting can be fussy. We broke a stock hub several weeks ago, but keep in mind these bikes are seeing some pretty severe use.
They are a joy to ride. The handling is incredible and power is great. The 400 handles like a 125 in tight stuff, the 650's are, well, very, very fast. I actually haven't spent much time on the 470, but the 501 is my favorite.
Check out the Husaberg site for more information:
www.husaberg.org. I saw a list somewhere that showed all the improvements for the 04 models and just about every issue we've had was addressed. With KTM manufacturing behind them, hopefully the parts availability problems will come to an end as well.