I have been back and forth from 2 strokes to 4 strokes, from electric start pigs, to valve eating CRFs. Finally, I think I'm in love. I rode an '06 YZ450 with off road suspension on some gnarly trails yesterday and bought an '07 today! (anyone want to buy a YZ250?). This thing has NO vibration, starts with a light smooth kick, turns like it's on rails - yet feels planted, and tracked on the rough stuff like a champ. I was very impressed. Light and fast! I didn't want to give it back! The bike I rode happened to have a Rekluse, which I must admit was very nice when chunking up some rutted, rocky uneven big hills. I am still worried about the durability of these things, but man do they work nice! (The Rekluse that is). The bike is rock solid, and from my experience, these 4 stroke Yamahas seem to hang in there for the long haul. I can't wait to go ride some more!!