1. A method for targeting advertisements to users, the method comprising: using at least one computer system to perform steps comprising: receiving advertisements regarding job openings from a plurality of advertisers; receiving feedback from each of the plurality of advertisers about search results provided to the advertiser in a search conducted by the advertiser for a job candidate to fill a job opening; determining, based on the feedback received from the advertisers, implicit criteria that indicate hidden preferences of each of the advertisers about which job candidates to target with an advertisement of the advertiser; receiving feedback from job candidates about job search results provided to each of the job candidates; determining, based on the feedback provided by the job candidates, implicit criteria for the job candidates; creating a plurality of advertiser profiles, each using implicit criteria for a given advertiser; creating a plurality of job candidate profiles, each using implicit criteria for a given job candidate; comparing the advertiser profiles and the job candidate profiles to generate relevance scores and determine matches between the advertiser profiles and the job candidate profiles; determining which of the advertisements received to present to each of the job candidates based on a relevance of each of the advertisements to each of the job candidates and a value of each of the job candidates to each of the advertisers based on the relevance of each of the advertisements to each of the job candidates; and presenting for display to each of the job candidates at least one of the advertisements determined for the job candidate.
1. A method for targeting advertisements to users, the method comprising: using at least one computer system to perform steps comprising: receiving advertisements regarding job openings from a plurality of advertisers; receiving feedback from each of the plurality of advertisers about search results provided to the advertiser in a search conducted by the advertiser for a job candidate to fill a job opening; determining, based on the feedback received from the advertisers, implicit criteria that indicate hidden preferences of each of the advertisers about which job candidates to target with an advertisement of the advertiser; receiving feedback from job candidates about job search results provided to each of the job candidates; determining, based on the feedback provided by the job candidates, implicit criteria for the job candidates; creating a plurality of advertiser profiles, each using implicit criteria for a given advertiser; creating a plurality of job candidate profiles, each using implicit criteria for a given job candidate; comparing the advertiser profiles and the job candidate profiles to generate relevance scores and determine matches between the advertiser profiles and the job candidate profiles; determining which of the advertisements received to present to each of the job candidates based on a relevance of each of the advertisements to each of the job candidates and a value of each of the job candidates to each of the advertisers based on the relevance of each of the advertisements to each of the job candidates; and presenting for display to each of the job candidates at least one of the advertisements determined for the job candidate. 18. The method of claim 1 , wherein the implicit criteria for the advertiser are inferred from actions taken by the advertiser on the search results provided to the advertiser.