For those of you who are using the ajax powered Google search plugin for your WordPress 404 page that I featured here Add Google Ajax To Your WP 404 Page, you may have noticed after upgrading to WordPress 2.3 that the search results have stopped displaying. A number of others including myself have experienced this problem and the fix is relatively simple.
In your WordPress admin panel, click on the OPTIONS link. Now click on the AA Google 404 link which will load the options for this specific plugin. Where it says Google API Key, click on the GET ONE link. Type in your URL to Google and they will provide you with a new API key. Replace the plugins current API key with the newly acquired one and click the save button. Your 404 search results should reappear.