My copy of Cyberduck crashes while in the background on OS X 10.5. Unlike all other OS X applications I've used, there's no notification when Cyberduck crashes, so when I save files from my external editor (BBEdit), I don't notice they're not actually saving over FTP. In some situations, this leads to lost work. I don't have any additional information about what's happening when it crashes, because I only notice it after the fact.