Ability to store SMSes on an IMAP folder would be nice. I consider SMS a different priority than IM. IM I tend to just wipe when I don't need it. SMSes I'd like to keep for a longer period.
As my imap server gets backed up daily this makes it the nicest way of doing it.
Edit: added forum link
http://talk.maemo.org/showthread.php?p=428885