I've been on Facebook since the beginning, in 2005. I explored it and studied it. I always spent minimal amount of time on it, though. I get e-mail notifications and perhaps once a day go there to click on all the "Ignore" buttons for all the invitations. So, I do not see is as a big time drain. But every now and then I get useful piece of information there, or an invitation to something I want to attend. I also use it to monitor what my kids are doing there. It is also nice to reconnect to some people I have not heard of in 20-30 years and see what they are doing.
I am on my third set of friends now. The first - lots of people at NCSU I used for the study linked above - got unceremoniously dumped once the study was done. I did not know 99% of those kids and was not interested in their activities. The second cohort were people with Yugoslav last names. I explored their habits - most of them are expat kids, some of them still in the Balkans - and saw that they friended each other regardless of ethnicity: Serbs with Croats with Macedonians with Bosnians, etc., they joined the same Yugo-nostalgic groups (lovers of chocolate bananas, or Djordje Balasevic), and generally frowned upon overt displays of nationalism. I saw that and liked it: the parents screwed up, but the kids are OK. Then I dumped them and built my current cohort out of bloggers, scientists, tech/PR folks, etc., with just a few remaining ex-students, Yugoslavs, old high-school friends and, more recently, lots of family members.
And I use Facebook not just to connect to people, but also to promote myself, my blog, my events, and my employer - pure PR, which sometimes works (as I can see from comments, traffic coming from there, etc.).
danah boyd and Fred Stutzman got dissertations on this topic, studying social networks. And no, "friend" online does not mean what many newbies think it means. Throws off some people initially, I know. It's a contact. On FB it's called 'friend', on Twitter it's a Follower, on FriendFeed it's a Subscriber, etc. FB friend is as friendly as your blog's RSS feed subscribers, or they can be real friends - this is up to you and your individual use.
On FB, you can separate your contacts into groups, e.g., family, Real Life friends, colleagues, old highschool friends, blog-friends, customers, potential customers, etc.
Facebook has evolved over the five years. Initially, FB was for college students only, soon highschoolers were added as well. They tended to friend people who they were RL friends with, hence the origin of the name. Initially, kids used it for social networking: finding people they know, their RL friends to organize parties, share homework, and keep in touch after graduation.
A couple of years later, bloggers, techies and PR-folks joined FB at the time new apps were introduced. They used it for business networking - promoting their brand, finding like-minded people, political organizing, etc. The two groups (~20s and ~40s) tried to stay away from each other, as the two style of FB use clashed.
This bi-modal distribution of FB users got disrupted over the last year - lots more 25-35-somethings joined in as well as non-tech, non-bloggy, non-business oldsters - the non-tech savvy: your Mom, your highschool friends who have otherwise no presence online... This new cohort is using FB in a middle-way, bridging the two groups already there. Some of them use FB like highschoolers - for social networking, organizing parties and flirting. Others use it like us - for business networking, organizing conferences and meetups, etc. Some combine the two quite well and are bridging the divide between the two older cohorts.
But they differ from the older cohorts by their use of communication tools on FB: the two older cohorts use Walls, Groups, Pages, Events, etc., i.e., all public spaces. The newest cohort is old-timey in that way: once they friend you, they prefer to switch on the privacy shades and Direct Message you on FB, or even switch to e-mail or Skype - their notions of privacy as they change in the 21st century are not well developed yet.
Facebook is great at finding people. It is not as good for finding things: data, information, people who are interested in same things. At about the same time - over the past year or so - blog/tech/PR types discovered FriendFeed which is better for finding people interested in the same things. Until then, FB did that job OK, but FF does it better. FB for those people is like a not-so-boring version of LinkedIn now.
So, Facebook has its utility. It does not do everything for everyone, but it has its place in the ecosystem of online social networks. And it is flexible enough that everyone can adapt Facebook to his or hers own needs. There is no one right way to use it.
Facebook is also a good tool for spreading the word about Darwin's 200th birthday! Check out this group:
Can we find 200,000 by Feb 12 to wish Darwin a happy 200th birthday?
I made an exception to my general rule not to join "I bet we can find X people who...." groups and joined this one. Highly recommended! As I write this, they are at over 111,000 members.
One difference between facebookand friendfeed: pseudo-privacy.
a localized version of friendfeed exists on some of the more "social" blog sites like livejournal. in both facebook and livejournal, i can and do have limited control over who can actually read what i write, look for my picture, or even find me at all.
while for myself, that's all unimportant and most of what i do is public anyways, i have friends that use livejournal as a rant against the occasionally stupid aspects of their work, and say things that while harmless in the bigger picture, will tend to piss off some types of people in management and the job is then at risk. similarly, some in management (in spite of laws against this) will take political commentary and points of view they disagree with and use that against an employee (sometimes just subconsciously - oh, he's a "liberal" and the label then taints all future interpretations of someone's actions).
some are thus so concerned about not having anything they write be taken by an employer out of context that they simply make EVERYTHING private to just the trusted friends on that particular social site.
services like friendfeed (I was playing with an idea similar to that about 4 years ago but lacked the time to put it together) require that everything be made public. there are many that can't or won't allow that.