I just accidentally uploaded my PGP key in unencrypted format to rsync.net. As far as I know, nobody but me has access to the account. Is my key compromised?
Compromise is not a binary thing.
It comes down to what's acceptable risk, and what's the consequence of a breech.
Is the key compromised if stored on a laptop left at the hotel room when you go out? I would for my personal keys say no - it's a risk I'm willing to take, because it's unlikely that it protects anything so valuable. If you're a spy up against a intelligence service, this may very well be a compromise.
You have to decide how much trust you put in rsync.net, how valuable the data protected by the key is, and how difficult it is to replace the key.