One of the things about Facebook that intrigues me is how you can see certain activity of friends of your own friends. (In my case, this is extended somewhat by the fact that I often see Jason on Facebook, which causes me to see things that I normally wouldn't see on my own account, but it's a similar situation.) The result of it is that I begin to recognize names and pictures of people that I've never met before. Last night I was at one of Jason's fraternity's parties, and I met someone who I wasn't certain if I'd ever met before. I'd seen him on Facebook, so I knew his name and what he looked like and other small tidbits, but I didn't know for sure if I'd ever seen him in person. (I had a feeling that I hadn't, and that turned out to be correct. Turns out he's a cool guy. I guess it wouldn't have made a good post if he sucked.)
Certainly there have been many times in my life where I wasn't sure if I was meeting someone for the first time or not, but in many of those cases I'm usually wondering whether I truly hadn't met them, or I had and they just hadn't made an impression on me. I guess the most similar preexisting social situation before this Facebook phenomenon is the scenario in which you meet someone's spouse or significant other after having heard of them several times before, but even in that situation, you generally haven't been seeing pictures of them beforehand.
I'm pretty terrible with names and faces, and Facebook actually helps with that too. It tests me with flash cards of a sort a little bit every day. There have been people that I've worked with for months for whom I still can't remember their name all the time, yet certain random people I don't know on Facebook I can recall in a snap. (This is easier at work now because I get photos of people who send me email, right in Outlook.)
For a shy, introverted person like me, this is one of the cooler parts of Facebook. One of the hardest social barriers I have to pass is getting from knowing nothing about someone to knowing a little bit about them. That awkward section of introductory small talk is still very painful to me. But meeting friends of friends is notably easier post-Facebook: I can go to a party of mostly people outside my own circle of friends and already know the names of some of the people there. And, since I've already gotten a little bit past that initial barrier, it's easier to gather the energy to talk to them, and it's easier to remember who said what. For a website often blamed for ruining our society's ability to interact with each other on a personal level, Facebook really seems to be helping me out.