phaolo: - delete messages:
umm.. why? Is this really needed?
If someone is a scammer, I prefer to keep the messages to remeber how he behave.
Also, if people starts deleting conversations, there won't be any sure proof for anything anymore. O_o
Well clearing messages could have other purposes. For example, if you had a PM conversation with someone that you'd rather....not be reminded of, for whatever reason.
That said I only used the clear messages thing once, when the old PM system was up. Other people's needs may vary.
And as JMich said, if you clear messages they are only deleted on your end, the other user still has them unless he/she deletes them too.