I had an '02 Kawasaki that came with Amsoil in it, but switched over to Mobil-1 at the first service interval. Amsoil is the other true synthetic and I've heard some good things about it from other bikers, but it just doesn't have the 20+ year track record in the extreme conditions and applications of a worldwide market that Mobil-1 does. I'm more sold on facts, and if I hopped a flight to McMurdo Station and looked in their maintenance shop the only thing I'd find there is Mobil-1 and Delvac-1. Listening to a bunch of weekend riders on a Sunday cruise yap about some other product just doesn't carry the same weight. Looking in shops that maintain equipment that costs mega-$$$ where downtime is not an option, well that's what makes an "endorsement" in my mind.