Logicmail was on my list to test this weekend
They want to switch from Treo 750w phones to BB due to reliability issues with the Treo and the lack of storage on them. Even with a 2gb card they run out of room - the roadwarriors think it's desktop email in their hand, not a mobile mail reader. Not that it'll be better with a BB.
Outlook on WM5/6 suffers from a 'broken' IMAP implementation also. No sync of sent or deleted items.
Checked into Versalink - they balked when I asked about multiple account sync.
ChatterEmail fits the bill but a PalmOS phone seems like a step back.