New
#10
I think the Beta is Feature complete - with regards to the major changes at least.
Assuming Microsoft listens to the Beta testers as they did with Win7, I would expect to see a number of minor functionality changes and maybe a few UI changes.
It's often the minor things that make the difference in gaining user acceptance - I think Microsoft now realise this
In My Opinion
As Office will actually effect far more users that even Win7, being installed on XP and Vista machines too.
I think that it will not be released until it's absolutely right - I can see another Beta and then an RC before it goes gold.
Chance for a few changes and a good reason to wait till June
It's just that Microsoft have a number of major conferences during the year - PDC and the like - If you check when the big one is in June 2010 it's likely that the official release will co-inside with a big conference.
Of course Technet subscribers normally get access to the RTM several weeks before the actual release - So you should be OK with a June release - even if it's at the end of June I would expect it to be up on Technet by the end of May