BuddyPress.org

As r-a-y points put, Mark Jaquith, one of the few lead developers for WordPress, was hired to build a highly-customized version of WPMU + BuddyPress for Gigaom. Mark of course is intimately aware of the intricacies of the WP codebase and I’m sure had an easier time customizing the project than would the vast majority of coders.

But, the Gigaom site does demonstrate what is possible with WPMU + BP if you are willing to become well-versed in the codebase or have deep-enough pockets to hire out professional talent.