Recently I worked on a partner project that integrated a third party search engine with Sharepoint (MOSS) 2007.  The most interesting use case in the project was to construct a custom component to replace the search bar in the Sharepoint site page headers.  The component was to be designed to access the third party search engine, which had been configured to crawl the Sharepoint content store.

It's an interesting use case because, in general, Sharepoint is not designed to easily integrate components into the Master Pages that govern the header display.  Sharepoint readily accepts Webpart components into the content areas of the pages, but the Master pages are not Webpart enabled.  Also, there is already a default search bar incorporated into the Master Page header as a ContentPlaceHolder, and it doesn't go away easily.  The project was even more interesting because I used the Microsoft Ajax Toolkit in my custom component.  As you might