The bans nominally last 24 hours. There was a point where there were so many IPs running (from AWS servers) they overflowed the ban list and the bans were shorter!
We've had a few guys using Amazon Web Services and continously rotate IP's/set up new instances - unfortunally, the last time we went too 'hard' on them - effectively making Posterous unavailable.
We're thinking about this right now. Feel free to hang around #preposterus on EFNet for updates.
