Business Week feature an excellent chart that neatly sums up the state of the web wrt to the US audience.

They divide the web audience into six categories:

• Creators publish web pages, write blogs, upload videos
• Critics comment on blogs and post ratings and reviews
• Collectors use RSS to gather information
• Joiners use social networking sites
• Spectators read blogs, watch videos, listen podcasts
• Inactives are online but don’t participate in any social media

The audience is also divided into 7 age groups:

• 12 – 17 yrs
• 18 – 21
• 22 -26
• 27 -40
• 41-50
• 51-61
• 62 +

The chart then shows you what percentage of users fall into each category and each age group. For example:

34% of 12-17 yr olds in the US, who are online, are creators. 51% of them are Joiners and 34% are Inactives (obviously, these categories are not mutually exclusive, so you can belong to more than one)

On the other hand,

only 5% of the 62 yr+ age group are Creatives, and 70% of them are Inactives.

Gives you a good understanding of who is where doing what.