Facebook's early growth was based in large part on tactical open-ups of the service. They started with just Harvard (where I'd say the "who's got the most friends?" game kicked things off), expanded to the Ivies and then elite non-Ivies (who desperately want to be like Harvard) and slowly, slowly worked their way down the college eliteness scale, adding similar types of schools at the same time (northeastern LAC's in one clump, west coast state schools in another, etc). Schools who weren't added yet wanted to be in the elite club, and schools that were already in were too busy editing other people's wall posts to notice the elite factor of the site diminishing. Eventually they opened it up to all colleges, but that was probably well after they had opened it up to the colleges that actually mattered, numbers wise. The college growth sorta has buttressed the rest of the growth, since it pulls in new users as they go to college and retains old users as they graduate.

Meanwhile, the site's features progressed along, making the site increasingly sticky (it really wasn't back in the day). The big hitters were and still are Photos and Events, which both happen a lot better if all of your friends are already signed up for the site.

All of this stuff happened well before there was a lot of hype from the Valley started kicking in. Facebook's growth since opening up to high school (and later, the world) is less interesting though, since they've basically been running on network effects, inherent virality and quality product. They didn't have any of those when the site first started.

Easy. Facebook was seen as the in thing on campus. If you had a Facebook profile, you were hip and cool and cutting edge. After a few months in 2004 it got to the point that not having a profile meant people simply forgot who you were (because they couldn't read your profile like they could everyone elses). Obviously it influenced none of your close friends, but people you just met would judge you by your profile and decide whether or not to include you in the future.

It was also a great way to find your friend's hot friends and set up a meeting somehow.

The fact you had to give them your college email address and a password was no barrier. Heck, not having to choose a user name or design your profile yourself made it easier to sign up.

(I can answer this since I was in college at the time it got started.)

I don't think you've really answered his question. If not having a profile meant people simply forgot who you were, then you're talking about a time when facebook was already big.

well there was transition. when people realized, hey i can invite everyone to my party and not actually have to go around inviting people or posting signs around campus. if you weren't on facebook, you weren't finding out about the parties. simple.

really, every decision of the masses can be attributed to laziness?

At the point when Facebook was a viable substitute for posting signs, there must have already been a lot of people using Facebook.

Refer to my first sentence (Facebook was seen as the in thing on campus. If you had a Facebook profile, you were hip and cool and cutting edge.) to answer his question directly.

I can only explain everything after that to me being a blustery gasbag that likes to elaborate.

Facebook the new AOL?

Absolutely the best analogy.

Has anyone written a Facebook App that gives Usenet access?

I'm going to write one that sends you free cd's with "software" on them.