I don't really understand why it's so bad. I mean, MySpace looks fucking dreadful but oddly it's a more pleasingly laid out design.
Everything in Facebook looks clean and neat except not together. Maybe it's the stupidly narrow central column design, but as soon as you start adding in this plug in applications your page looks awful: too much information, too many little links.
It seems masterful in a slick design managing to fail to be remotely 'nice'.