Well, thanks all for the replies.
Nice link, Bugtussle.
It looks like I'll be trying a full synthetic then. And since my bike wants 10/40 oil, I should avoid the slipping clutch issue Circletree was having using 10/30 synthetic oil ( At least according to the article Bugtussle provided a link to).
I just figured synthetic oil is a (relatively) cheap way of providing a little extra protection in an air cooled engine, where I guess the oil can take more of a beating than in a liquid cooled motor.