It’s official now, Google has put their AdSense for Feeds into beta. They’ve got a FAQ about it, a brief “best practices” article and an application to sign up.
There will undoubtedly still be those who thing that this is just the worst thing to happen since the dawn of time. I think this is more or less a natural progression. Just like many in the entertainment industry (music, movies, tv, radio, etc) didn’t (or chose not to) see the future coming and find ways to make it work for them, those who fight against this idea are in for a long loosing battle. Instead of trying to fight it the better road is find ways to make it work for everyone (see iTunes).
The writing is on the wall, ads in feeds are here, get used to it or get out out of the way.