Bill Gates, Seinfeld ads barely match up to any of the user-generated ads I have seen over at YouTube. IMHO, $300 Million would be better spent on crowdsourcing Microsoft's ad campaign. There are some really cool ads out there, here are a few:
Why would you pay $300 Million? Why bother if the whole Seinfeld ad is pulled off or not! -- when you can let your users champion your cause.