I've spent the better part of two days testing this, and I have to say it's a great, great thing. It plays friendly with existing installations if it has to, but I think once people get used to seeing how this works, and the way (like donncha mentioned above) that this allows people to break free from a single forums section and turn this into forums with purpose, it only makes sense to let BuddyPress do the work.

The way that BuddyPress is developed also opens the door for other plugins to tap into the forum creation API, so it's possible to have forums that aren't just for groups, but maybe events, or blogs, or any other type of object that is centered around users in a group-esque fashion.

This isn't a 100% complete setup yet, as there isn't a forum directory or a global tag search yet, and things like forum/subforum relationships or groups with multiple forums aren't implemented. But, it's safe to assume that much of the bbPress functionality will be mirrored in BP by the time 1.1 comes around.