8. A system for ranking Web pages in a Web search engine, the system comprising: at least one processor; a communication interface; and a memory containing a plurality of program instructions configured to cause the at least one processor to: receive, via the communication interface over a network, a Web search query from a particular user, the Web search query including at least one keyword; identify one or more Web pages that contain the at least one keyword; determine, for each of the one or more Web pages, a raw page ranking; adjust the raw page ranking of each of at least one Web page among the one or more Web pages based on direct evidence of how interesting the respective Web page is to users to produce an adjusted page ranking, the direct evidence being derived from clickstream data collected from the users; and present, as search results, the at least one Web page to the particular user in accordance with the adjusted page rankings, wherein the direct evidence of how interesting a Web page is to users includes a measure of how often the users traverse to or from the Web page in browsing the Web and a measure of how many users have recently visited the Web page compared with how many users normally visit the Web page, and wherein the measure of how many users have recently visited the Web page compared with how many users normally visit the Web page is given greater weight than the measure of how often the users traverse to or from the Web page in browsing the Web.
8. A system for ranking Web pages in a Web search engine, the system comprising: at least one processor; a communication interface; and a memory containing a plurality of program instructions configured to cause the at least one processor to: receive, via the communication interface over a network, a Web search query from a particular user, the Web search query including at least one keyword; identify one or more Web pages that contain the at least one keyword; determine, for each of the one or more Web pages, a raw page ranking; adjust the raw page ranking of each of at least one Web page among the one or more Web pages based on direct evidence of how interesting the respective Web page is to users to produce an adjusted page ranking, the direct evidence being derived from clickstream data collected from the users; and present, as search results, the at least one Web page to the particular user in accordance with the adjusted page rankings, wherein the direct evidence of how interesting a Web page is to users includes a measure of how often the users traverse to or from the Web page in browsing the Web and a measure of how many users have recently visited the Web page compared with how many users normally visit the Web page, and wherein the measure of how many users have recently visited the Web page compared with how many users normally visit the Web page is given greater weight than the measure of how often the users traverse to or from the Web page in browsing the Web. 12. The system of claim 8 , wherein the plurality of program instructions are configured to cause the at least one processor to adjust the raw page ranking of each of the at least one Web page in real time in response to the Web search query.