This excerpt taken from the UNTD 10-K filed Mar 1, 2007.
We compete for advertising revenues with major Internet service providers, content providers, large Web publishers, Web search engine and portal companies, Internet advertising providers, content aggregation companies, social-networking Web sites, direct marketing businesses, and various other companies that facilitate Internet advertising. We also compete with television, radio, cable and print media for a share of advertisers total advertising budgets. We believe the primary competitive factors for Internet advertising are size of user base, the amount of time users spend on a site, the ability to target advertisements to users and the demonstrated success of advertising campaigns. We believe we compete favorably in each of these areas, although certain competitors have a competitive advantage over us as it relates to the sale of advertising on our social-networking and Internet access services.