Social-networking users are a fickle bunch. Friendster used to be the most popular of the new breed of Web 2.0 destinations, but before long it fell out of vogue and people stopped going there.

In its place, MySpace became the darling of the web. MySpace provided not only a free place to host your own online identity, but a full set of tools for meeting and interacting with others.

Now everybody is talking about Facebook, which fits the same description, but in a very different way. Will Facebook become the next MySpace?

I think so, and here's why.

First, the social networking phenomenon proves that vast numbers of people (and not just the highly tech-savvy) like having their own outpost on the web where they can show what they're all about, communicate with friends, and mix with new people.

To be sure, MySpace is far bigger than Facebook. Almost 25 million people visit MySpace every day - about three times the number who visit Facebook daily - and MySpace racks up about 46 billion page views every month compared to Facebook's 16 million.

But as the people at Friendster learned, things can change quickly in web culture. Social networking sites appear to be unusually transient businesses - a bit like social clubs in the real world. Every couple of years or so a different club becomes incredibly popular, and everyone starts going there, leaving the previous year's hot spot nearly empty. That's human nature, and it dominates the virtual world, too.

MySpace and Facebook differ in some significant ways. In terms of membership numbers, Facebook is quickly catching up to MySpace. According to some analysts, Facebook is adding members at three times the rate of MySpace. It's achieving that rate of growth by becoming something more than a site for college-age socialites - which is exactly what Facebook was until last May, when it opened its doors to anyone with an email address.

Since then membership has shot up by 89 percent to about 27 million users, versus MySpace's 60 million. Much of that growth has come from people in the post-college age group (ages 25 to 34), which burgeoned by 181 percent between May 2006 and May 2007, internet research firm ComScore says.

Facebook: the mature alternative

Facebook isn't quite a mass-market phenomenon yet; most people who are familiar with the site run in college or technology circles. But the buzz around Facebook is loud and well pitched, suggesting that the mainstream audience is just now learning about Facebook and sees it as a more mature alternative to MySpace.