Well I'm a great fan of the web clips feature of Gmail. I'm not a heavy user of rss feeds but I use web clips to keep track of about 10-15 blogs.
Gmail has now added a new advertising feature to web clips where sponsored links are rotated in the web clips bar. They're marked as such but I think they'll convert much better because people naturally look there for a link of interest if they're bored, unlike the other adsense style ads. (The sponsored links are, of course, contextually related to the email content.)
They don't actually show up beside web clips, they're displayed as a web clip by themselves. The only difference being that the text "web clip" is replaced by "sponsored link". When there's no ad available a "gmail tip" is there instead. Cycle through the webclips when you're viewing an email and you should come across one.