I had IMAP on my 8830 for a little while, if you use IMAP between you BlackBerry, Web Interface, and Desktop client it will not sync from BlackBerry to Desktop or visa-versa.

However it will sync read/unread messages from Web Interface to BlackBerry, as well as deleted items. (Which we have already have, deleted items that is)

There was a delay of about 10 - 15 minutes with the IMAP.

I would recommend staying with POP, IMAP has no real advantages at this time. (There were a few threads in the general discussion forums, I would read threw that if you want more information on the BlackBerry IMAP configuration)