I keep my home directory in a Subversion repository. A month ago that repository broke down. Subversion developers were unable to help me without access to the repository, which I didn't want to grant, since my repository contains some private data (Jabber account passwords and the like).
I spent a day debugging the problem until I found the cause (a loop in a data structure). Then I was too busy to do anything, and a month went by without regular backups. Two days ago I finally hacked a workaround and managed to extract a nearly complete repository dump. All is well again, except for my confidence in Subversion, which is a bit shaken.