Pew Internet has a handy page up showing the current demographics of US Internet users. It includes...
Who's Online
A frequently updated table showing the current demographics of Internet users.
Online Activities - Total
The percentage of Internet users who have "ever done" an online activity.
Online Activities - Daily
The percentage of Internet users who do a given activity on a 'typical day.'
Internet Adoption
A chart showing the change in U.S. Internet penetration over time.
(Via Jeff Jarvis.)
