I like facebook because it allows me to connect with all of my friends in one central location. Rather than e-mailing each one individually about a party I can send out a facebook invite and my friends can ask questions, comment to each other, say what they plan on bringing (so others don't bring the same thing) and potentially get rides either there or home.
It is also a great way to share pictures of events that we all participate in. One or two of us will take pictures of everybody, put them on facebook for our friends to download at their leisure.
Not to mention that facebook also allows me to connect with friends and relatives that live far away from me.