According to MacNN:
Microsoft has begun sending out invites for the Office for Mac 2011 beta, a shared e-mail indicates. Participation is being limited to people signed up with the Microsoft Connect service. The company is in fact enforcing a strict non-disclosure agreement, blocking leaks through “all forms of communication including print, broadcast, electronic, Internet publications, social media networking sites, blogs, and verbal disclosure.”
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, and implement advanced document collaboration features. Microsoft has confirmed, though, that the suite will be 32-bit only, since not every component has been converted to Cocoa.