BuddyPress.org

@armandmorin

WP 3.0 merges the functionality of WPMU into standard WP.

BP 1.3 will support WP 3.0:

https://buddypress.org/about/roadmap/

@wordpresschina

With WPMU, you can use some nifty BP plugins like BP Group Wiki, BP Group Blog and BP Classifieds. These plugins do not work with the standard WP version of BP.