1. A method of generating targeting parameters of a media buy plan for an advertising campaign including one or more advertisements to be displayed in conjunction with presenting web pages, based on a history of search events, comprising: receiving key phrases relative to a subject of the advertisements for which the targeting parameters of the media buy plan are to be generated; providing the received key phrases as proposed key phrases to determine, from search events indicative of historical data of uses of a search service, a first subportion of search events for first queries of the search service that have been received from a first sub-population of users and a second subportion of search events for second queries of the search service that have been received from a second sub-population of users, the first queries including one or more of the proposed key phrases and the second queries not including one or more of the proposed key phrases; applying classification processing to determine potential targeting parameters that, statistically, contribute to membership in the first sub-population of users that have submitted the first queries of the search service including one or more of the proposed key phrases and contribute to membership in the second sub-population of users that have submitted the second queries of the search service not including one or more of the proposed key phrases, wherein the potential targeting parameters include one or more user characteristics, the user characteristics including demographic data; associating statistics with the potential targeting parameters, based on the historical data, indicative of factors usable to determine whether to use the potential targeting parameters as the targeting parameters of the media buy plan, wherein the targeting parameters include one or more characteristics of users to be targeted by the media buy plan; and generating recommendations regarding the media buy plan based, at least in part, upon the statistics associated with the potential targeting parameters, the recommendations indicating whether to use at least some of the potential targeting parameters as the targeting parameters of the media buy plan.