Was Facebook Down? Basically, Yes
Facebook Is Down In All Practical Terms
While Facebook's servers are not currently offline, the social networking site is basically down. the source for http://facebook.com simply shows as <html></html>.
[Update: Facebook is no longer down: looks like they found the missing 100% of the site's code]
This is probably not Anonymous taking action for Facebook founder Mark Zuckerberg being declared TIME Magazine's 2010 Person of the Year over Julian Assange. Far, far more likely is an error in porting some fix or other, resulting in... emptiness.
This is a case in which Is It Down for Everyone or Just Me fails, alas.