If you want to know what the top search terms are that land people on your site or blog, you want Web analytics software. There are some good and comprehensive tools out there, such as VisiStat. But there's another valuable way to use search engine results: the new HitTail service.
The service attempts to divine what your site's visitors are "trying to tell you with the language of search." It looks at the search terms that got visitors to your site but still show up low on search engine results lists. HitTail posits that if you write more about these terms, you'll get more traffic from search engines.
This is a very clever idea, and during the free beta period, it's worth trying out if you write a blog or run a commerce Web site that has a blog attached to it. Be warned that there is a lot of cultish prose on the site about the Long Tail effect and the certain riches that will come your way if you use the service. Try to look past the hype and focus on the interesting and valuable information that HitTail offers.