Sam Sethi offers this analysis
RSS has effectively eliminated the potential value of AdSense and DoubleClick because the majority of people never view them. This is already hurting publishers who rely heavily on the income generated by people watching or clicking on adverts... Therefore I think it would be a smart move by Google to acquire FeedBurner, simply because Google could then start to serve their own ads (Adsense or DoubleClick) into the RSS stream.
The comments on Sethi's post are good, too.