Microsoft has begun sending out invites for the Office for Mac 2011 beta, per some readers of Test ToT. Access is being limited to people signed up with the Microsoft Connect service. MS is enforcing a strict non-disclosure agreement to be part of the beta.
The completed suite is due to be released later this year, and should carry over a number of changes in recent Windows versions of Office, such as the ribbon interface. It will also drop the Mac-only Entourage software in favor of Outlook for Mac, and implement more document collaboration features.