You're right. As of today, I am not offering any RSS feeds that include advertising, but I would like to experiment with it in the future. My feeds today are partial "link feeds", where you get the question and a clickable link back to the Web page that contains the answer to the question.

If I were to offer an RSS feed with advertising included, I'd structure it differently and have a full-on feed that included both the question and answer, but probably slipped the ad between the two sections or at the very bottom, to be minimally disruptive.

That's a key best-practice though, I think: if you are going to include ads, make sure that your RSS feed has greater value to offset the increased annoyance that subscribers will feel because of the presence of advertising. Syndicate the entire article.

Other best practices that come to mind: don't include more than one ad unit in your feed articles, something that isn't discussed on the Google AdSense for Feeds terms of service (see my AdSense info) but will probably end up being prohibited anyway at some point. Plus, it's annoying.

Finally, Google itself recommends that you include a page on your site that details the terms and conditions on the use of your feeds, which isn't directly related to AdSense for Feeds, but it's still a darn good idea.

Hope that helps you create a great alternative RSS feed that includes your adverts, and that they perform well for you!