Yeah, gotta be careful with respect to maintenance. I crashed earlier this summer because I shifted my chain into the spokes, locking the rear wheel in a turn. I
knew the limit screw was set improperly, but I figured it was not enough to cause any problems. Well, I was wrong. I landed on my leg, though, and unclipped quickly enough that I didn't even scratch myself too badly. (Threadlock is your friend, BTW, so the limit screws don't unscrew themselves. I still pull the derailer cable before each ride to make sure the chain can't be shifted off the cogs, though.)
Also, did you use your front brake? I tend to see my rear brakes as a backup; I use it if the front brake fails, if the front wheel has poor traction, or if I'm descending and just want to slow the acceleration. The front brake can develop about 5x more stopping force, since the front wheel can't skid. And, if you are used to using it, you won't go over the handlebars in an emergency. http://sheldonbrown.com/brakturn.html