When the Internet Explorer team first introduced the Search Box next to the address bar in IE7, we also introduced an easy way for users to install search engines offered by websites that they visit. Users who want to add a site's search engine to the browser's search box can do so with just two clicks.
Building a Search Provider XML file is pretty easy for web developers, but for fun, I put together a little Internet Explorer Web Search Provider Builder tool that generates the XML file based on a simple web form. A few months after I built this tool, a new PM on the IE team was tasked with taking my sloppy ASP code and making it into a formally supported feature, posted on the official IE Search Guide page.
Unfortunately, the official Search Guide's builder feature was removed in a site redesign late last year (it wasn't very commonly used). Folks who want an easy way to build a search provider may simply use the original tool, found here: http://www.enhanceie.com/ie/searchbuilder.asp.
<personal anecdote> The new PM referenced above became my wife just over three years later. 🙂 </personal anecdote>