John Battelle's got an interesting slide up from comScore showing that heavy search users, while making up only 20 percent of those searching, are responsible for 68 percent of all searches that happen. See it here: Search Volume by Type of User.
Conclusions? Depends on your angle, I guess. If more of us become heavy users, then there will be more searches happening, making advertisers who want more traffic happy. But solving the supposed search inventory problem isn't necessarily a solution for search engines. Lack of inventory may actually help them earn more per click.
Want to discuss that more? Visit our thread on the topic: A Drop in Search Engine Ad Supply.