Facebook is a social networking site. Its the one that ends up in the news a lot because people think that their invitations to a "red plastic cup" party remains secret despite being on the Interwebs. The cops/people-who-weren't-invited look at these go to/call in these parties and then the news swarms all over it.
Premise: 9/10 Its a good idea too be able to keep up with all of your friends without having to actually talk to them. This ultimately saves you the time and money that you would have spent calling them or hanging out with them. BUT when real people see a good idea guess what happens. They want to break its goodness. Namely eCreepers, Most "Friends (despite the fact that they don't know eachother)", and people who stay logged into it for multiple hours.
Look and Feel: 8/10 Its pretty plain but on the Interwebs that can be a good thing. Look at MySpace. That is why the HTML should be locked. Forever.
Connectivity: 9/10 The servers are usually up but sometimes they get excessive traffic.
Other Stuff: 4/10 They have a sorts of games and stuff you can put on your profile. But they all require you to spam your friends with invites to them. Some of them are good, but a lot can be boring.