This functionality is most commonly used to search the Internet using search engines like Google or Live.com. I recently was reading Scott Hanselman's blog and found an interesting entry on how to let your visitors add your website to their search bar. In a nutshell, you need to provide information on how to search you site in an XML file according to the OpenSearch standard. Next, reference this file in the head element on each web page in your site via a link tag. When a user visits your site their browser detects this information and allows the user to add your site to their browsers search bar.
