As usually, Danny Ayers has some great thoughts on the Feed Subscription debate. Here's my response, which I'll trackback over to his blog entry.
This has nothing to do with icons, although it would be nice for the user to be able to recognize the button. You could put an anchor around the text "Subscribe". That anchor points to your RSS file and has the correct media type. For RSS to cross the chasm, all the i's have to be dotted and t's crossed.
Autodiscovery is definately the way to go. But it's only part of the solution. Returning the correct media type is another part of the solution. I really like your XSL solution. That's definately another part of the solution that I hadn't considered. But, consider that most users will be terrified to find 20-30 subscription mechanisms to choose from. The mundane user would move on and you'd have one less subscriber. On the other hand, if there was exactly one subscription mechanism, then you'd have yourself a lot of subscribers.
