Oh good, i thought this thread was about woman problems.
I had about 100 private messages (too lazy to delete them) in my folder which all went after the change. Doesn't bother me about the size being smaller. Surely there's no need to keep them.
Deletion of PM's now is a bit (well just initially) confusing, having to select delete from a dropdown box that says move as default. Maybe it should be on delete as default.
Yes, to save room and to provide something more for Premium users in the future. You guys have probably missed the option to download PM's as a text, XML, or CVS file in the bottom right hand corner of the PM page. This allows you to archive old messages for future reference, so you can delete them off the site.