10. A computer system for fetching a web page, comprising: means for creating an index for use by a search engine, wherein the index indexes a set of previously crawled web pages; means for determining which queries, from a set of queries that have been previously submitted to a search engine, qualify as needy queries; wherein said needy queries are queries for which the index does not currently index adequate, relevant content; means for estimating an impact, on said needy queries, of fetching a particular uncrawled web page by comparing terms of said needy queries with at least one of: (a) an anchortext of links, obtained from the previously crawled web pages, that point to the particular uncrawled web page, and (b) a Uniform Resource Locator (URL), obtained from the previously crawled web pages, that points to the particular uncrawled web page; means for ordering web pages to fetch by a web crawler based, at least in part, on the estimated impact, on said needy queries, of crawling the particular uncrawled page.
10. A computer system for fetching a web page, comprising: means for creating an index for use by a search engine, wherein the index indexes a set of previously crawled web pages; means for determining which queries, from a set of queries that have been previously submitted to a search engine, qualify as needy queries; wherein said needy queries are queries for which the index does not currently index adequate, relevant content; means for estimating an impact, on said needy queries, of fetching a particular uncrawled web page by comparing terms of said needy queries with at least one of: (a) an anchortext of links, obtained from the previously crawled web pages, that point to the particular uncrawled web page, and (b) a Uniform Resource Locator (URL), obtained from the previously crawled web pages, that points to the particular uncrawled web page; means for ordering web pages to fetch by a web crawler based, at least in part, on the estimated impact, on said needy queries, of crawling the particular uncrawled page. 11. The computer system of claim 10 , wherein the means for estimating the impact of fetching the particular uncrawled web page further comprises means for combining a query-based estimate and a query-independent estimate for said particular uncrawled web page by computing a weighted average of said query-based estimate and said query-independent estimate for said particular uncrawled web page; wherein said query-based estimate for said particular uncrawled web page indicates how well said particular uncrawled web page meets neediness and relevance requirements of the needy queries and is determined based, at least in part, on the anchortext and the URL that point to the particular uncrawled web page; wherein said query-independent estimate of said particular uncrawled web page is determined based on query-independent features of said particular uncrawled web page.