We're just testing Exchange 2010 and I was surprised to find it (mostly) working after migrating a user.
BES 4.1.6 (MR3)
Noted issues:
Meeting invites are not received in the BB inbox, left as tentative and still requires processing in Outlook.
Any updates to meetings done on the device fail to send.
Creating new meetings from device fail to send to attendees and do not sync to Outlook.

Sending and receiving of emails appears fine.
Contacts, Notes and Tasks synch'ing also appear fine.

Anybody have any update on when this will be officially supported?