When someone's online activities come back to embarrass them offline, I always just roll my eyes. It seems silly that anyone could be surprised that tweets, blog posts, or photo sharing comes back to bite them. You put it on the internet, man, of course it’s public.
Start-up social networks of any sort easily fall prey to a huge hurdle. Without a strong, active userbase, all the clever design and clear UI in the world can’t make a social product a success. If a user posts a question, shares a photo, or interacts with the product in whatever way the designers intended, and he doesn’t make a social connection, there’s no network.