I have just started using it and I must say I am impressed. However, one of the things I would find really useful is monitoring a mail folder in my exchange mailbox. I know this can be done, so I have tried a few times, but I find that it takes too long to update when new mails appear. In my inboxes (I monitor two - one exchange and one IMAP, both through outlook) the messages appear in sidebar within a few seconds, but what I do is move certain messages to another folder using rules and if I set up a sidebar panel to view that folder, I find it can take a couple of hours to spot mails that have been moved there.
I have tried playing with all the settings, but it doesn't seem to make any difference.