Wow. I'm so lazyweb, I hadn't even written up the post describing the app i wanted, and someone's already gone and built it. Jon Aquino made YubNub, his entry in the Rails Day contest. It's a server-based system for assigning your own keywords for automating queries and searches. Jon describes a bit about the app's creation on his blog.
In my mind, the version of this application I'd want to create would be installable on an intranet, so we could make specific keywords for our environment. (For example, we use FogBugz, so typing in "bug 3524" should go right to that bug's page in the system. The best way to do that, in my mind, would be to have YubNub (or some intranet equivalent) understand Mycroft (or Sherlock) plugins, as well as Dave's Quick Search Taskbar Toolbar Deskbar plugins.
If you could import the XML files that power those search services, it'd be really easy to populate the service or application with a bunch of search syntaxes that are already created.
At any rate, Jon's app is well worth checking out, and I'm sure it'll be evolving to include more features in the future.