OK, I love Facebook. I am addicted.
I hate MySpace.
Why?
Facebook has learned from the mistakes of MySpace and designed a system from the ground up. They have created a better system (not a better mouse trap, because we all know what happens to the mice when you put traps around).
Facebook has help create a system which has built-in, one of the things that their users need the most: boundaries (or whatever metaphor you would like to use: firewalls, curtains, shields).
Facebook isn't perfect. It is a human system and no matter how intelligent the design, it still falls short. I realized that today when I tried to create a Facebook account for my son, Carter. The Facebook system told me he was not eligible for an account. Fine, there is probably wisdom in that.
however, as a father, I want the first social networking account that my son has to be one that I create and approve of. If I have to explain that to you, you aren't a parent.
I will say this and it is something that is so completely obvious to one generation and may take a lot of explaining to another. There is power in whoever can come up with the social networking software that has "Facebook features" and appeals to multiple generations.
Why? Because grandparents will give anything for a good picture of their kid and his kid. (References available upon request).
Addendum: Did you know that Facebook and Myspace aren't in the Blogger Spell Check Dictionary? ;-)