My first EIC at InfoWorld, Michael Vizard, used to argue that a market is greater than two and less than 10. By that definition, RSS advertising looks to have become a real IT marketplace with eWeek now in the game pioneered by InfoWorld. As Steve Rubel observes, eWeek is running its RSS ads as a separate entry. So you'll be scanning headlines in your newsreader and stumble across a clearly identified advertising headline that, if clicked, takes you off to the full text and/or associated vendor links.
Matt McAlister at InfoWorld argues in a comment on Steve's post that readers don't like dedicated ads in their RSS feeds, and would rather have them embedded within individual entries.
Now that we have two US IT publishers experimenting with the model, we'll start to get a sense of who's right based on repeat business and blogger feedback. My hunch is they are both right.