I have a Buddypress multi-site called http://www.extrafriends.co.uk that at the moment sits behind a login forcing people to register before they can see any content. Its powered by the Genesis theme framework and has a number of your other plugins on it too.
For its next iteration I want to create a homepage where only the homepage is visible to visitors. So if a logged out user clicks on any part (I'll be featuring everything from Marketpress items, Q&A posts, forum posts and Buddypress activity) then they are forced to login or signup - which'll be handled by Gravity Forms.
So the flow would be, visitor browses to the site, can see the widgetized homepage but if they click on anything they see a login/signup screen.
Can membership do that?