Adding to your comment, it's my understanding that many people feel the site is poorly designed. I've often heard "I wish there were an easier way to..." in relation to facebook.
What are some other sites that lay people use and that do as many things as Facebook does?
Yeah, I hear people (usually on Twitter, often right after proudly mentioning how rarely they use Facebook) commenting negatively about Facebook's UI, but it's pretty rare that I see somebody point to a site that does the same things and does it better.
Funny. I remember one of the main reasons for the adoption of Facebook vs. Myspace was "Cleaner looks, better usability". Last thing I heard Myspace is still around, and I guess so will be Facebook, once someone else takes over their lead.