The PMs system is a bit messy and updating it is something that's been in the pipeline for a while. It requires a lot of work so we've been holding off while we get other things sorted (like the Local etc). We'll take a look at it again soon though, as we agree, it's not very user friendly.
As for deleting/editing your own posts - it's not really something we're looking to implement, mainly because it would cause complete havoc. You're welcome to ask us to remove a post for you (by reporting it to us).