As Dave Winer notes, proliferation of feed subscription links is getting out of control. Every web-based RSS aggregator has its own way of presenting a link to give the user one-click subscription, and there’s very little compatibility. (Syndic8 has around twenty subscription links for each feed.) For pure desktop aggregators, feed: URLs work well – your aggregator registers for the feed: scheme, and gets the URLs from any feeds that you click on.
Dave proposes a server-side solution; it’s a neat idea, but my feeling is that passing all feed subscription through a single domain name is liable to cause problems somewhere down the line: registrations lapse, business models change; a protocol is far stabler and more flexible than even a well-written general service. I’d really like to see a movement to get support for feed: URLs deployed as widely as possible. That way, users are always in control.
It seemed like this would be really easy to add to Firefox, which has a great cross-platform extension mechanism, and indeed it was. The Feed URL Handler extension handles clicks on feed: URLs and delegates them to your choice of online service. So, as long as users have this (or something like it) installed, you only need to put up one type of subscription link – and of course, at any time, users can migrate to a desktop aggregator. Remove the extension, and let your local application deal with feeds directly. This also means that Radio Userland (I think the first app that I saw with that technique of direct browser interaction), as well as other aggregators, can now take advantage of feed: URLs as well as custom subscription URLs.
Unfortunately, requiring universal rollout of a standard is both simplistic and unreasonable (users without any handler installed will get a cryptic error about an “unknown protocol”), but with pretty much everyone pushing to get their search and browser enhancement software on as many machines as possible, as well as Firefox’s simple extension management, it seems like this is the kind of additional functionality that could be of real benefit in making feed subscription quick and simple.