At the end of the day, the real problem with using ComScore #'s when developing a media plan is unlike with all other forms of mass media (TV/Radio/Print), in Online the advertiser has direct feedback from the audience of their advertisements - hence you don't really need to use a 3rd party measurement service to help you determine if your campaign was on target/"worked".<p>A much better way to buy media online is sprinkle money around, see what performs best, allocate more money there, measure, test, repeat.<p>ComScore was designed to meet the need of old world media buyers working in online - those who can't wrap their heads around allocating media $ based on actual placement performance, rather than a 3rd party measurement company's estimate of what the audience might look like. There are A LOT of these people out there - hence ComScore has done OK for themselves. Unfortunately I agree that over the long term, their importance in the world of media buying will dwindle, and they will become more of a competitive research tool used by middle management and tech bloggers to re-enforce their viewpoints.