How cool is that!?
What is OpenSearch you might be asking??
OpenSearch is an attempt to standardize search methodologies to share search results across platforms, engines, etc. Its more complicated than that or than I care to explain.
What it allows IE7 and Firefox 2 to do is add a search box to the browser that can be customized by users to search any site they want. The little tutorial posted at unto.net explains how to have your domain automatically added to that box (the user still has to opt in to making your domain a permanent addition to the list) so the next time they use it, they can easily search your site.
If you have IE7 or Firefox 2, checkout your search box, you’ll find SEO’Brien available to add.