Though certain advertisers can currently succeed at RSS advertising, advertisers who buy RSS advertising to reach the masses right now shouldn't set their expectations very high.
Given the low adoption rate, you might be able to guess the typical RSS user profile: college-educated males, 18-34, with above-average household incomes. If you're thinking of buying RSS advertising now, keep this demographic in mind. ...
RSS's main advantages are that it's a spam-free, opt-in, direct-to-consumer, economical means to deliver information. Who wouldn't want to exploit it?
At 2 years old, advertising in RSS feeds is still in its infancy. Specialized feed-management companies, such as Pheedo, FeedBurner and Feedster, offer advertising solutions, while Google and Yahoo now both syndicate contextual search ads in RSS feeds. Ads may be purchased on a CPM or CPC basis, depending on whom you use, but the number of publishers willing to serve ads in their feeds is an obstacle. Expect to see this change as publishers lose eyeballs to their feeds and, by virtue of their own business models, must make up the lost ad revenue by adopting RSS advertising.
-"Too early for RSS advertising?" by Hollis Thomases, ClickZ.com, Feb. 28