I finally got to understand what RSS auto-discovery was good for by perusing this example page  [found thanks to David], which points to Mark Pilgrim's Radio auto-subscribe bookmarklet. Once you have this bookmarklet in your link toolbar,

Whenever you visit a site that you want to add to your Radio news aggregator, click your "Subscribe" button on your link toolbar, and it will try to find the site's RSS feed and auto-subscribe you.

If you're using Radio, you can try it out here, on this very site (note the sneaky tactic to get more subscribers). It worked for me, at least on the home page. Of course a problem is that not all weblogs support auto-discovery. In the worst case the button seems to just do nothing.

If you have no idea what I'm talking about, you could start on my page on personal news aggregators.

This bookmarklet makes adding RSS subscriptions to Radio a breeze!!!