Yahoo has issued a new white paper on RSS. You can download the PDF but here are some key findings:

• 12% of users are aware of RSS, and 4% have knowingly used RSS.
   
• 27% of Internet users consume RSS syndicated content on personalized start pages without knowing it’s RSS
   
• 28% of Internet users are aware of podcasting, but only 2% currently subscribe to podcasts.
• Even
  tech-savvy "“Aware RSS Users"” prefer to access RSS feeds via
  user-friendly, browser-based experiences (e.g., My Yahoo!, Firefox, My
  MSN).

World news and national news are preferred at 52%. More specialized content such as blogs
(23%) and podcasting (11%) are gaining. So basically, it’s mainstream media rather than niche content that gets the most use.

The primary benefit reported for use of RSS is efficient access to media sources.

Publishers
striving to syndicate their content via RSS should pay attention to how
their feeds are listed within popular RSS readers since that is the
preferred method to discover and subscribe to feeds. Publishers should
also
provide easy and prominent means for users to add RSS feeds on every
article page.

27% of Internet users subscribe and read RSS feeds without knowing being aware of RSS as a format. These "Unaware RSS Users" are
similar demographically to the average Internet user, suggesting that
RSS is not only for early adopter techies.