And finally, when a user searches for certain broad and popular subjects (the band U2 or a health condition like diabetes, for example), Bing will show, in addition to the usual blue links, a navigation bar on the left-hand side that breaks down the results by category. Bing decides on these subsections based on previous combinations of queries; each one links to a secondary search.

In the case of U2, these categories include "images," "songs," "tickets," "merchandise," "downloads," "interviews," and "video." In the case of diabetes, Bing shows results in the following categories: "articles," "symptoms," "diet," "complications," "prevention," and "test."

"We are going to compete hard on the core results, but where we are going to differentiate is in organizing results more effectively and providing tools to help searchers make decisions," says Weitz.

Google is still the 800-pound gorilla, with 64 percent of the U.S. search market, compared with Microsoft's 8 percent, according to ComScore. Yahoo, the second-largest search engine, has 21 percent. Google also claims to have the largest Web index of all, and that in just the past year, it has increased its collection of indexed documents by "billions."

Google wouldn't comment yesterday, only saying, in a statement, "We welcome competition that helps deliver useful information to users and expands user choice. Having great competitors is a huge benefit to us and everyone in the search space--it makes us all work harder, and at the end of the day our users benefit from that."

According to Weld, there's still plenty of room for both Google and Bing to improve. "Search can and will get much, much better," he says.