for me, my trifecta would be imap+caldav+carddav support on android.
there has been some recent activity on the bug list for android on talk about caldav support, so if you are interested, i'ld star this issue to keep tabs on their development:
Issue 2361 - android - Add support for external calendars via iCal / CalDav - Project Hosting on Google Code
and with carddav coming out in 6.0.1 things just might come together...