I have no problems with the concept of Ad Supported RSS, but I have a lot of problems with its poor execution. Case in point, 2RSS. They recently added advertising in their Atom2RSS service. But they’ve trashed the signal to noice ratio in doing so.
I recently added a low volume, blogger provided feed to my subscription list. The only subscription link on the page went through Atom2RSS. And after going through the backlog, Atom2RSS injected six consectutive ads into the feed with no new content.
Compelling content might support one third advertising (by both number and footprint). I suspect that one fifth will prove a better threshold for most of us. If you want to stay in my reading list, then mind your signal to noise ratio.