Feedburner blog has posted about the launch of Adsense for feeds this week, i don’t see them in lot number of blogs except TUAW feed. As they said they may launch it incrementally for all publishers.
If you are a feedburner Ad network publisher sitback and relax the ads will roll out some time if not now. Default feedburner ads will run as usual along with these new contextual Adsense RSS ads.
If you are not participating in feedburner ad network you can still run feed ads from Adsense account. Also you will be able to control ad frequency and other things from your adsense account.