1. A computer-implemented method of formatting content on a user network site, comprising: receiving format preference information for the user network site from a network site administrator, the format preference information defining a format preference of the user network site; identifying format performance information comprising performance metrics of advertisements, each of the performance metrics based upon a performance of a particular advertisement positioned at a particular advertisement location on network sites having a particular format; based upon the identified format performance information, determining advertisement locations on the user network site that optimize a performance metric of advertisements presented on the user network site; determining a document format for the user network site based on the format preference information and the determined advertisement locations; dynamically adjusting the document format based on changes to the format preference information or the format performance information; and formatting the user network site based on the adjusted document format.
12. The method of claim 1 , further comprising: providing an electronic document in response to a request for content accessible at the user network site.