PR Opinions has a story on RSS and tracking. I can understand why people want to know who is and isn't subscribed; subscribed readers are more committed, adn - in a sales/marketing context - may be more open to learning about the products and services you provide. It's interesting that outfits are starting to look at that, but the 'solutions' are amusing:

So when I read that IMN Inc (formerly iMakeNews) have announced (PDF only) a trackable RSS feed service I was intrigued. A way of tracking RSS success.  Fantastic.

However, when I went to their site, and from the story in ClickZ it seems that all they do is publish your content to an RSS feed and count the hits.

"We've encoded all the links -- usually with an RSS feed you get a subject of an article and a link. Every link provided is a unique trackable link. When you open up the feed we know it. Every time you refresh the feed we count it. And when you click to read a particular article we register that," Goodwin said

Heh - that's just scanning logs and counting, something I do in my free time for entertainment value.