Sorry, but I don't buy it - we will have to disagree on this one.

Let's one thing straight, to begin with: popularity of a service does not equal quality - people have many reasons for using Facebook, but the quality of user experience that it offers isn't necessarily the major driver for uptake. (Peer pressure is a much more likely explanation, for one - see Jean's experience, for example.) One of the best historical examples for this are video recorders, of course - eventually, the VHS system won the race against Beta not because of its superior quality, but because it was better marketed and more content was available for it (which also translated into peer pressure). So, whether Facebook is "well used", as Elyse puts it, has fairly little to do with whether it provides better social networking tools than its competitors.

Beyond this, though, your descriptions of Facebook's friending system seem to make my point for me: ultimately, everything comes down to a simple binary choice of 'friend' or 'non-friend'. That's what's at the core of Anonymous's "if you don't know someone - don't add them": I don't have the option to add them to my network in a more limited, more nuanced way, as 'not-quite-friend'. Yes, I can add someone as 'friend' and then add a note saying "well, actually, they're not really my friend", but that's ultimately meaningless: in the first place, that person is now listed as my friend, and whatever I've added as a further description for that person has no significant functional consequences in the Facebook system.

Which, again, indicates to me that any finer distinctions beyond the 'friend'/'non-friend' choice on Facebook constitute little more than afterthoughts in the system right now. Give me a more fully featured system that enables me to distinguish different communities of friends more effectively (school friends from colleagues, family from neighbours, people in the various interest groups that I belong to from one another), and I might think differently...