Ok, so 0.8 should be somewhat useful, but code is a piece of crap...
So, 0.9 is declared devel and some of my ideas for it:
- some OO design
- support for more DB's (at least PostgreSQL)
- better plugin system
- new address book with LDAP support
- if PHP team puts imap_thread() into the stable release (patch is already there), threaded message viewing...