Don't be obnoxious.

Facebook has obvious problems as a company—privacy violations, data retention, lock-in, and so on—and as software, especially with regard to the frequency with which it's buggy as hell.

However, it's also had more impact on the utility of the web for most users than almost any other product, save for perhaps Google. More than one-seventh of the entire human population now uses Facebook every month, which is incredible. And to achieve that in only 10 years—obviously by providing a service that many people feel is worthwhile—is still something that we can admire, regardless of the other issues around Facebook.