1. A computer-implemented method comprising: receiving first query terms from a user; automatically selecting, based at least in part on the first query terms, and from among a set of documents, first documents; automatically generating second query terms based at least in part on anchor text that is contained within links that occur within the first documents; automatically selecting, based at least in part on the second query terms, and from among the set of documents, second documents; wherein the first documents differ from the second documents; automatically generating third query terms based at least in part on anchor text that is contained within links that occur within the second documents, and not based on any input from said user; and automatically selecting, based at least in part on the third query terms, and from among the set of documents, third documents; wherein the third documents differ from the first documents and the second documents; determining a first number that is a number of documents in an intersection of (a) a set consisting of the first documents and (b) a set consisting of the second documents; determining a second number that is the first number divided by a number of documents in the set consisting of the second documents; determining whether the second number is at least as great as a specified percentage; and in response to determining that the second number is not at least as great as the specified percentage, automatically generating the third query terms based at least in part on anchor text that is contained within links that occur within the second documents; wherein the step of generating the third query terms is performed by one or more computing devices; and wherein said first and second documents are not displayed to said user.