Steven even posted the necessary registry entries for Internet Explorer to wire up an application to respond to a user clicking a link like this. So, for example, NewsGator could add a subscription whenever a user clicks on a feed:// link.
This seems like a reasonable idea to me…with the obvious benefit that a user could just click on the link, and the aggregator could add a subscription to the feed. As opposed to the situation today, where if the user clicks on a feed link, they’ll see (at best) a page full of XML. Now of course they can right-click on an existing link, and select “Subscribe in NewsGator”, but supporting a left-click subscription as well might be nice.
Other aggregators support a subscription link in a format like http://localhost:5678/…, but I dislike the idea of applications listening on certain ports like this. The feed:// idea is much more attractive, IMHO.