I don't really know about that. Myspace is still probably more popular, but ever since Facebook was opened up to highschoolers and then everyone (it used to only be available if you had a college e-mail address) it has become popular to. I prefer facebook but I keep a myspace too.
The only real difference between Facebook and Myspace is that Myspace allows you to customize your page with HTML. Which presents huge security holes, and insures every teenager out there goes and makes the shittiest page imaginable with the same generic Myspace page generator. It's been called the ugliest site in the universe for a reason.
Facebook isn't customizable. Therefore, everything looks boring, but everything looks clean. Sorry, this is the one area of my life where I act like a conservative. Also, those annoying songs don't pop up on every page you visit.
Man this explanation is a lot longer than I originally planned.
Ok cool, thanks for the update.