BuddyPress.org

Firstly, to put profilt to root directory : define ( ‘BP_ENABLE_ROOT_PROFILES’, true );
This will get the the url of http://mydomain.com/username
Secondly, multisite issue. Go to Dashboard/Super Admin/Sites/Edit/Permalink Structure
there you’ll see the annoying “blog/” structure. edit it. That’s all.
Thirdly, the problem– What if somebody in your network create a blog “cat”, and your root blog have a category of “cat” ? No solution for this yet, wait WP 3.0.2