Jeff Bertolucci of the PC World has this fascinating article titled Search engine shoot-out: How we tested the search engines. It says:

We tested a total of 55 services in six categories: general (text info), video, mobile/local, news, images, and blogs. We conducted our tests over three weeks. We used ten terms in each category. For general text-information searches, for instance, our categories included technology, pop culture, research/academic topics, books, and travel/shopping. In each category we posed what we considered an easy query and a difficult one: Just about every search engine could find the 2007 Academy Award winners, for example, but only a few could locate a portrait of Italian poet-philosopher Giambattista Vico. We tested the engines at different times of the day--morning, afternoon, and night--on all seven days of the week.

We performed all of our testing on the same Windows system, a 2-GHz Celeron desktop with 512MB of memory and a 1.5-megabits-per-second (download speed) AT&T/Yahoo DSL Internet connection. We didn't test for query speed, but this typically varied by only fractions of a second. Among the most-popular search sites, we saw little difference in between the time we pressed Enter and the appearance of the search results. However, we did detect significant differences among the blog-search engines, with some smaller sites--such as Best of the Blogs--taking several seconds to post the results. For the local-search tests, we used a Nokia E62 smart phone.