[Adam Harley (Kawauso)]

Most integration issues I tend to see are related to deep integration, rather than straight forward user integration. I guess it boils down to, does bbPress transfer over existing users to WP’s user tables cleanly (or at all) if you integrate it post-install. It would be possible to do manually anyway, since their respective user tables are essentially identical in structure, but bbPress users would have no WordPress meta whatsoever.