A few days ago, I manually reset one of my computers during a Dropbox update. What I didn't realise at the time was that it would cause files that were halfway downloaded to be subsequently uploaded in a corrupted state. Fortunately, three things allowed me to fix it: Dropbox has a previous versions restoration feature, the corrupted files were uploaded at zero size and I was able to write a program to search out empty files to manually restore. Crisis averted!
Mokalus of Borg
PS - I've never been so thankful for backup before.
PPS - One of the affected files was my blog drafts backlog.