[sabj]

From friends who have worked at FB (in particular, both FB and Google) they report that the culture is a little strange and affected: Mark and others put a big emphasis on the importance of their 'hacker culture,' but try to create said culture through the exhortations to protect it... [?]

Anyway, I can't vouch for Facebook one way or another, but I can say that Google certainly has a very strong culture, although it waxes and wanes depending on where in the company you may be, and can take on different characteristics by business function. Also, you really can only get a certain snapshot by visiting, versus actually working there!