In 1996 UIE started conducting research on web sites with on-site searching capability. At the time, we noticed that many of the implementations weren't very good, returning results that didn't help users find the information they needed. Jared M. Spool subsequently wrote: Why On-Site Searching Stinks.
Over the years many things on the Web have changed. On-site searching, however, still lags behind. We still see users struggling with on-site search, so much so that we started hearing the same thing over and over again in our studies: "If Google can do it for the whole web, why can't this site do it for itself!?!".
Well, it turns out that much of the power of Google's Search comes from the fact that it indexes the entire Web. By taking into consideration all the links coming into a web site, Google can judge the relevancy of each web page very well. We've found that we use Google endlessly in our work.
When it came time to place Search functionality on our web site, we considered whether to build our own or simply use Google. So we built a prototype using it, and we were really surprised. It works as well if not better than some of the customized systems we've tested on big-name web sites costing thousands and thousands of dollars!