I'm the worst what-iffer and I tend to think about the worst thing that can happen, which finds me walking the bike at times. I certainly feel that the reason I'm gaining confidence is because I originally learned how to fall and how to bail with a good set of knee/shin pads. Last season I slowly weaned myself off of them (except for riding the rockiest places).

Also, as was mentioned, it's all about momentum. Often going too slowly will get you in trouble more often than going fast. The best thing that my boyfriend/mechanic told me was that "you've got 26" wheels and a fork and a frame that were designed specifically to hit all of this gnarly stuff. Take advantage of it and trust your bike to pull through when you need it to." And it usually does!