BuddyPress.org

@john:

Your option 1 is a standard BuddyPress install structure. (although themainblog is probably better referred to as sitename)

Your second option is in two parts – nameofablog.sitename.com is again the standard BuddyPress / WP subdomain install.

buddypress.sitename.com/members/ does not fit in though. It would be http://www.themainblog.com/members as per your option 1.

Each blog can have their own theme. The BP admin bar can be shared across the top of all blogs, or removed on a blog by blog basis (a call in the blog’s template file – functions.php)

So, to summarise, the standard BP / WP subdomain install is:

http://www.sitename.com – the main blog
http://www.sitename.com/members (etc.) – the social network elements – profiles, directories, etc.
anotherblog.sitename.com – a member’s or other blog on the site

You can style the main blog pages to look different to the social network pages (although they are using the same theme: different template files / CSS, etc.)

Each additional blog can have it’s own completely independent theme

The admin bar can be shared across the top of all blogs

Hope that helps, Roger