I was uploading a page after adding some minor edits, and got an 'oops' error, with an ftp issue (log showed it couldnt log in although its working fine on the previous 10 uploads in the previous 10 mins, it was a obviously just a minor glitch). Anyway, the file happened to be index.html and was no longer on my host - just a partial file called 'pureftp something'. No sign of the actual file. I had to restore from an old offline backup.
How can this happen! Without my backup I would have been screwed!