I just bought a 2007 everyone I know who had them like them and said there very dependable. Its kind of a low option simple ATV so there not much to go wrong. Also it has a super reliable simple air/oil cooled motor Yamaha has been using for over 20 years in many other ATVs and motor bikes.
Here is some owner reviews on it Vehicle Reviews for 2006 Yamaha Bruin 350 Auto. 4x4
Seems like its just a simple "gas and go" machine, thats the reason I bought one.
Love how it turns on a dime compared to my full size 500. Much more fun on the narrow twisty trails.