On the issue of whether to introduce a new URI scheme to allow one-click feed subscription, in spite of W3C Technical Architecture Group's position against new URI schemes, I am adding my vote to Dare Obasanjo's proposal which is already in fairly wide use.  While I understand W3C TAG's position, a less than ideal solution is better than expecting the world to accept the right solution.

If you are unfamiliar with this issue, Jon Udell has a post with links and words.

Update:

I should note that neither schemes address the need to support multiple aggregators at the same time.  I thought about writing a general feed subscription management plugin for IE but haven't found the time yet.