BuddyPress.org

We’ve alreayd figured out how to do it, like I said above.

““* Members will have to fill in their profile details for each site. I believe that’s the case… unless that can be shared, too?”
The point is to have it *not* shared.

“* Each sub-domain would have to be upgraded separately””
No, they will not. One install, one plugin, one upgrade.

“So being that there is a field when adding content to the activity_meta which includes the blog number (usally 1), and there is an option in the activity table to ‘hide_sitewide’, what needs to happen to make it work across blogs.”

No, not blog_id. the relevant portion is site_id.