Last year, one of our mentors was whacked in the head by our ramp, which wasn't properly fastened while we were moving it at the BAE regional. It wound up cutting part of his head open, and the EMTs had to stitch it back together (either 7 or 9 stitches as I recall.)
So the lesson is, the EMTs at hand at competitions are VERY useful, and it's a REALLY REALLY good thing they are there.
As for myself, the worst is probably some gashes, soldering burns, the usual splinters and pinches, and of course, the typical programmer's memory leaks and overflows.
Jacob