Facebook observation
My experience with Facebook has been great. I'm somehow engaged with Facebook nearly every day -- sometimes multiple times a day.
Of course I'm there not only as a participant, but as an analyst. That changes the experience. Think of it this way -- if you read several books on the subject of writing books, then your book reading experience changes. You no longer merely enjoy the story, you find yourself following the techniques the author has employed to impart life to the characters, develop the plot, maintain through-line, manage tension, build a believable world, and more.
So, as a social computing person, I find much to study in Facebook. Consider this: Facebook, through the use of shared applications, allows friend networks to define their own fluid experience/identity. Put another way, affiliations are defined not only by friend status and group memberships, but by the applications people share. Facebook apps are introduced by any member, then compete in what I suspect could be drawn as a classic fitness landscape. Usage equals survival.
I believe "ownership" of the apps in play at any time, across an affiliated network of friends, is a key ingredient contributing to the stickiness of the experience. That leads to the following social computing design principle: users own the experience. Give them building blocks, not finished experiences.
Of course, many of these general purpose social apps give users control over their UI. Interestingly, Facebook doesn't do as much of that (wall, superwall, html widget, and some other examples, aside) -- certainly not like MySpace (or Piczo, which I think has a great UI for simple customization). With Facebook, identity is defined through a balance of expression and affiliation -- affiliation beyond "see my many friends".
Imagination exercise: consider the tier-three design model I proposed earlier (as an essential reframing -- broadening -- of the social computing phenomenon). Next, superimpose clouds of shared social apps on top of and relating the connected people icons -- indistinct edges and all. You might start by imagining one app at a time. Now maybe you're seeing what I'm seeing. Don't let that worry you, it's not permanent. You'll feel fine in the morning.
What I find curious is that they haven't attempted to reinforce the shared spaces visually. Wouldn't it be interesting to experiment with ways of adding, to the individual's UI (opt in, of course, and with tools to customize), attributes that depict the affiliations in play?