Have you noticed that people older than about 25 are Facebook whores.  These people joined Facebook once it opened to the public (and not just for college students).  They are constantly posting pics, writing on their friends walls, updating their status, etc.

Here is an interesting article in the NYT about how young adults are a bit smarter about what they post on the site.

Some interesting facts of Facebook users in the United States:

# of people aged 13-17:

# of people aged 33-77: