Once fell off my RipStick mini at 10 mph and got scraped in four places. I hit my elbow on the pavement and got a pretty bad road rash there (gouged out about a 16th of an inch of flesh, half inch diameter). Also scraped my knee, another spot on the elbow, and my hip. And I was still half a mile from home. So I got back on my RipStick. On the way home, there's this steep hill that's part of a bike path. Rather than be sensible, I thought to myself, "Well, I've got nothing to lose now", (not true) and went down. Now, this hill gets you going 20+ mph coasting, doesn't matter what you're riding. Luckily I didn't fall on the way down, or I would've most certainly broken bones. I made it home, freaked out my parents a bit with the injuries (I tried to act like it was no biggie; they weren't buying it), cleaned it up, and was out of commission in terms of physical activity for a while.
Man, I don't know if I could live with myself if I permanently injured myself somewhere that prevents me from running around/Rollerblading. :(