Yo, i'm a pretty big facebook whore. Almost all my friends are people i know IRL, which opposite the case of EF. EF is used for having discussions, while facebook is used for keeping in touch. You can share photos and tag your friends, and also just write whatever you feel like on someone's wall. Facebook is also really good for inviting people to events; pretty much every party my friends throw is made into a facebook event so that it is easy to invite people and provide pertinent information.
As for the hookup thing, facebook is really useful for a situation where you meet someone you hit it off with, but for whatever reason you didn't leave with their contact info. Then you can search their name and add them, and shoot public or private messages back and forth - hopefully resulting in a future meat-up. EF i dunno about, i've never tried to creep any EF women.