BusinessWeek.com offers a nice chart of what people are doing online, broken down by generation (Forrester Research data).  The research defined the following roles for Internet users:
Creators – publish Web pages, write blogs, upload videos
Critics – comment on blogs, post ratings and reviews
Collectors – use RSS, tag content
Joiners – participate in online social networks
Spectators – read blogs, watch peer-generated videos, listen to podcasts
Inactives – online, but do not participate in social media