Playing like the big boys may be getting cheaper. The big boys, like YouTube, farm the serving of their most popular videos to a third party CDN. A lot of people were surprised YouTube didn't serve all their content themselves, but it makes sense. It allows them to keep up with demand without a large hit for infrastructure build out, much like leasing computers instead of buying them.
The problem has been CDNs are expensive. Om Malik reports in Akamai & the CDN Price Wars that may be changing. CDN service could be becoming affordable enough that you might consider using them as part of your scaling strategy.
Akamai, once the clear leader in the CDN field, is facing strong competition from the likes of Limelight Networks, Level 3, Internap, CDNetworks, Panther Express and EdgeCast Networks.
This commoditization may be bad for their stock prices, but it's good for website builders looking for new scaling strategies. EdgeCast, for example, passes on the cost savings when when their bandwidth costs drop. Other services lock you into fix cost contracts.
So competition is good. New cheaper, faster, and easier possibilities for scaling your website are coming on line. Maybe CDNs can help you.