In a recent poll that Johanna conducted, 61% of the respondents stated they didn't have a web site. Lots of these folks may want one, but don't necessarily have the time or money to invest at the moment.
The social networking sites like the ones you mention, Anne, are an interesting option for anyone who wants a web site that's free and easy to set up. It's usually as simple as registering a user name and then using pre-built modules (like photo galleries, guestbooks, etc.) to build your site. Best of all, no specialized computer programming knowledge is necessary.
I recently set mine up on Windows Live Spaces at abnleather.com, and thought it turned out pretty good for only a few hours of work. Maybe there's something to this whole social networking thing, after all!
Alex