Word each request precisely and use singular terms instead of plural ones. It may seem obvious, but some engines offer users a choice of languages for the search. If users don't click, say, English, the search will include sites in foreign languages. Using quotation marks around a phrase will help ensure only sites that include that phrase are found. For example, typing in pepperoni pizza on AltaVista brought back more than 81,000 hits.
People are afraid of Boolean.
It's frightening to them. And users don't always take the simplest route. Most people typed in the company's name in the word search field rather than simply clicking on the link. Sullivan uses to gauge a site is by just typing in a company's name. If it finds a link to the company, it gets a perfect score.