And so the inevitable monetization of RSS feeds begins. Don't be e*il, G*ogle! Don't mark all items in the feed as updated when there were no updates.

From Robert McLaws: FunWithCoding.NET - Longhorn Edition : AdSense in RSS - Explained.:

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So many of you might have already noticed that we have Google AdSense in our RSS feeds. I'm not going to go into detail on the how or why, at least not yet. But I do want to answer a couple of questions that have already come up:

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