I scanned the forums and didn't run across any of these that we'd like to see incorporated.
1) email export. We'd really like to see a feature like "export folder as mbox" or something like that. We like to archive project email to our server. Yes we could use an imap client or something and accomplish a similar task, but it would be nice to right-click a folder and export it directly to mbox.
2) contact as attachment. I was looking around and didn't see anything like this. I know 4.0 has the ability to share address books, but it would be nice to be able to send single contacts via an email attachment. If this is already a feature I had a hard time locating it.
3) turn off sharing. Maybe it's blindingly obvious, but I couldn't figure out how to disable sharing of a address book or calender. I think the only thing i coudl find was to share it in a different way.
4) multi-sharing methods for single item. it would be nice, for instance, to have "view only" for all and then be able to specify people who could edit, add, etc. even splitting up these tasks further. i.e. people can add, but not delete or edit, etc.
5) display all contacts when using To: search. Right now you can only search. it would be nice is you had the option to display all. Even a "blank" search won't return all. A search for "@" does, but that's not intuitive.
these features I think I've seen mention of, but I thought I'd reitterate it
6) personal distribution lists.
7) shared mail folders.