Facebook just achieves lock-in in a different way, AOL forced its subscribers to use their portal and aggressively tried to hook people by providing free samples. Facebook has captured enough of the market that people "voluntarily" only interact with their online friends through facebook, or rather they are forced to due to network effects and spend a significant amount of time consuming "content" and ads.

It also turns the dynamic of the web, where you actively seek out information through search and by following links, on the head, by pushing information to you, forcing you to at least acknowledge them. It has a similar ad-ridden, homogenous aestetic as AOL, practically unbearable without some ad blocker.