Facebook is completely different than MySpace. It was created at first for networking within colleges, and has just recently opened up to high schoolers.
I know with the college kids you need a valid university e-mail and must confirm it, so theres no way of getting around the "You must have attended school here" thing.
The high school site and college site are not linked, and high schoolers cannot friend college kids and vice versa. You must be invited to the high school site by someone who already is on the Facebook and is at your high school...I don't really know how that works since I'm not in high school.
I can tell you that Facebook is drastically different than myspace. No annoying music in the background, no obnoxious colors, kind of a simple survey profile and the option to put up pictures, join groups, and write messages on each others wall. While it's not completely innocent, (hey, it's a bunch of college kids, no one's photo album is going to be 100% innocent) it's not in your face blatantly out of control.
You can report people and their pictures as well.
Myspace is a WHOLE nother ballgame. I have one, and I know every friend in person. I hate it, I can't stand how obnoxious it is, but it is another form of procrastination

and some old high school friends found me on there.
I have a family friend's daughter on there...I am shocked at her profile. I remember being 12 and 13 too, but this was when AOL was practically the only form of internet and we weren't as completely intertwined with the computer as the younger generations are now. Her profile says that she's about 17, she comes across as incredibly self assured, and she has a new boyfriend each week (one, that I might add, she's "In LOVE with".