Re: latest version and WordPress Mu 2.7
I would go with WPMU 2.7 and buddypress beta 2 (which should be out really soon). If buddypress beta 2 isn’t released, I would come back and ask which version is the most stable out of trunk for your release. WPMU 2.7 is “so much different” than 2.6.5, so it would be nice to get users on it right out of the box instead of changing right away. There are loads of improvements since BP beta 1, but you have to get a development snapshot that works
Long story short, I doubt beta 2 of buddypress will be that long since the tickets are dwindling down….