I’ve got link icons using CSS that tell when I’m linking to the iTunes Music Store, and I seem to remember a plugin for Firefox or Safari that did the same thing for linking to PDFs, JPEGs, MP3s, etc. [Update: Found it, thanks to Scott] It’s more or less doable to have icons identify what form the information you’re linking to is in.
I want something more involved. Wikis generally identify links to external urls or pages that don’t exist with an icon. I want an icon when I link a Washington Post article that says to use BugMeNot.com to get a fake username and password. I want an icon on links to Salon stories that say you’ll have to sit through a 30 second ad before I can read the linked content. I want links to the New York Times to automatically include an icon and link to the New York Times Permalink Generator. Hell, if you want to really get out there, I want to know when a site has been hit by every major blog (except for Slashdot, which will hit the site two or three days later) and is overwhelmed with traffic so I should use FreeCache or Coral.
Basically I want a way to know what hoops I’ll have to jump through in order to read the linked content, so I know whether it’s worth my time to even click. I’m guessing that the rel attribute of a tags could be put to use for this, but there’d have to be some agreement of what terms to use. I suppose that the W3C could form a working group, which would offer a recommendation in two years that would unite the web in ignoring it. The other option is for someone to just build a plugin, pick their own rel attributes and tell everyone else to fall in line.