I spent an unexpected amount of time during a meeting today trying to get a little search interface I wrote to properly support opensearch autodiscovery and to get the "you can install this search in firefox 2 and ie7" thingy working. Then I just did the same for this blog's opensearch interface. In case you want to do the same (get browsers to autodiscover and two-click install search plugins for your opensearch targets), here are some hints. Note, though, that they might be firefox2-specific.
Here's the thing: getting opensearch-based search plugins for your browser can be a huge win for the visibility and usefulness of your resources to your user community. It's easy and it's great to have your stuff right there, an easy query away all the time. But if you want to make it easily auto-discovered, you have to get all the details exactly right *for* them.
That said, I'm not 100% certain it works in ie7. If anybody has it handy, tell me if it works for you?
Links:
[1] http://developer.mozilla.org/en/docs/Creating_OpenSearch_plugins_for_Firefox
[2] http://drupal.org/project/opensearch