I was a range officer for a carbine class put on by [url]www.pro-tac.net[/url] this Saturday and saw my first broken extractor.
This was on a well-maintained Colt shooting surplus 55gr loads. I got handed the rifle when it wouldn't extract (for obvious reasons) the fired case in the chamber. When I broke down the rifle, I found that the extractor had broken off just at the notch that grabs the case rim. We were at a range that has a gunsmith, and he had a new extractor, so the student was back on the range in five minutes.
No other real malfunctions in 8 hours of pretty steady shooting, although some folks were a little too stingy with the lubrication. I saw some non-GI mag bodies that flexed and wouldn't feed when loaded out to 30 rounds. This allowed the rounds to sit side-by-side in the mag instead of staggered, resulting in two rounds being fed at once.