I second that. I mapped a specific trackpad gesture to 'Command-W' (using BetterTouchTools). Now when I perform my crazy gesture on pages like http://www.hnsearch.com/search#request/all&q=hello or http://try.github.com/levels/1/challenges/1 , it prints a 'w' in the text bar instead of closing the tab. It really bothers me.

It has legitimate uses though, I'm not saying it shouldn't be used. But please use it only where it makes sense.