Sports stadiums are never profitable. Tax payers in the municipalities where the stadiums are built pick up the losses in almost all cases, either during construction or when the team decides to just leave and holds them ransom for a new one.
2/3 of restaurants fail outright soon after opening. The other 1/3 tend to be profitable really quickly (running a restaurant is tough and you can't run it at a loss for very long). You'll see successful restaurant owners start another one within a few years, because the old one is starting to get stale to people. Besides, around that time usually the star chef decides to move onto something better too.
Dance clubs fall into a couple of categories IMHO. You have the smaller spots, which can and do thrive. They hold about a 100 or fewer people, are often started by one really savvy entrepreneur who just wanted to create a cool spot (sound familiar to hackers and OSS? :-P). Then you have the bigger spots. These are cavernous mega clubs, and in my experience they're often in one way or another linked to organized crime and/or money laundering. They'll garner a lot of attention through PR, celebrity sightings, and marketing, and eventually implode under a pile of debt. How you can pile up debt selling alcohol at $7 a shot and several hundred dollars a bottle, I'm not quite sure. Read about Peter Gatien, one of the more notorious club owners in North America. Jay-Z has rapped about him: "Me and my operation, running New York nightscene, with one eye closed, like Peter Gatien". The whole business is about shifting debt like a hot potato. It's disgusting.
Social businesses have a finite amount of time with which they are fashionable to the masses and under which their growth is distorted. That first explosive growth trend never repeats itself ever again, which is probably what Facebook is trying to contend with right now as it decides when to go public.
If I were Mark Zuckerberg... I'm clearly not anywhere as brilliant as he is... but if I were in his shoes, I'd take a page from other successful social entrepreneurs. Start something new that's cool and is not Facebook-branded. The trick to social businesses is that the entrepreneur should be the brand. Facebook should be a Zuckerberg product in the same way that 69 Royal Hospital Road is but a single Gordon Ramsay restaurant. Zuck should have a portfolio of social sites, not one fucking behemoth that, when it fails, takes him down with it.