#Facebook. This makes Facebook a "walled garden". You have to have a Facebook profile or every now and then you find yourself excluded.
For me CompuServe was the original walled garden. It hosted information that I needed for my work. I had to use CompuServe, I had to pay for that privilege and I hated it because it was not that great an experience.
So far, Facebook finances itself by selling stocks and by selling adverts. There is a lot of speculation about future revenue streams following its recent IPO. Premium services that is services you have to pay for are already popping up and really what is more obvious than providing access to restricted content ?
At the time, people were afraid that the CompuServe model would make the Internet less open. Facebook is probably relatively as big as CompuServe was at the time. The best way to deal with walled gardens is to ignore them as much as possible and actively support diversity on the Internet.