I can't narrow this down, because the problem goes away eventually, but I keep running into situations while editing Ruby documents, particularly while modifying regular expressions (e.g. working with '/', '\', and '.' characters), where Sublime Text simply exits. No crash, only a little whimper in the Console:
08.05.12 15:32:50 com.apple.launchd.peruser.501245 Exited abnormally: Broken pipe
Relauching and attempting the edit yields an identical exit. At some point, I give up and use TextMate for a while. And then eventually it stops, until it starts again. This occurs with the most recent nightly, but it's been a problem I've experienced semi-regularly, with many versions.
I wish I could offer more information. Is there a log file I can send you?