Message Deletion
{warning:title=Warning} This is initial content taken directly from the mailing list {warning} Case in point - the OpenMicroBlogging protocol that La.coni.ca supports it but it doesn't appear to allow for deletion of messages sent to federated sites. http://openmicroblogging.org/protocol/0.1/
It appears that while La.coni.ca itself supports deletion of messages. This would have no effect on messages posted to federated systems unless they were only displayed as a link to the originating system (which the protocol doesn't appear to require).
Sounds like a pretty hard problem.