It's easier, surely you havefriends you don't speak to everyday??? Rather than having to call them all, or text them all to tell them some news you can just FB them.
If you want to share pictures (eg my frends wedding I wasnt able to go to, I saw her wedding pics on everyones pages, easier than everyone emailing me their pics).
I had a scan not long ago and it was quicker and easier to just change my status to '......is pelased her scan went well and everything is fine with baby' so all the people that wanted to know, knew.
Yes, zombies and the such like is pretty silly, but Facebook is a site that was created originally for uni friends to keep in touch, under the idea that you normally move in diffreent directions after uni, then it was opened everyone.
I'd think it sadder if someone stayed in the same little house in the same little town, with the same little friends and never branched out enough to have met someone they don't see daily.
Also, it's free, cheaper than a phonecall, cheaper than atext.