BuddyPress.org

You’ll get a better answer from others, but look into the posts about using the BP Theme Framework. Specifically, using a parent theme based on a WP theme with templates for Buddypress functionality added to a child theme.

Take a look at h-mag.com. Although this is more customization than most will attempt, this is what I’m looking at doing and really seems like it can be accomplished by making heavy modifications of the template files and lots of CSS work. The developer of that site can be found in the showcase thread.

Good luck.