I do see what you're saying, dutret, but - just to play devil's advocate - there are many ways to stress a frame. A lot more than what? Racing? Commuting? Loaded mountainous touring? Please qualify. We don't even know what his gear ratio was.

What I was saying to the OP is that under ordinary conditions, a decently made steel frame shouldn't crack. His cracked after 2000 miles. Good steel? Ehh... hard to believe it wasn't a preexisting structural problem in the BB area that revealed itself via the added stress of riding fixed. I put tons of miles on my fixed gear bike, which is a total gaspipe beater Paris Sport that had lord knows how many miles on it when I converted it, and with a little TLC have had no problems, commuting every day in NYC, mashing up the hills of VA where I'm working right now, etc.

Steel... my old Puch's frame bent after going over a huge pothole at night... so badly the front wheel was almost touching the down tube - it was the classic warping by where the top tube and down tube meet the head tube. Still rode it all over till it was stolen. Only problem was bad toeverlap, otherwise it rode fine. Granted that bike didn't have the added stress that a fixed gear will cause (due to the mashing you mention), but it nevertheless had years of hard all-weather riding on it.