You're going to lose access to a LOT of sites that use the Akamai Content Distribution Network (CDN).
It might be better/easier to implement some type of content filtering, perhaps using OpenDNS?
I can remember trying to block multiple Akamai networks during the broadcast of the 2008 Philadelphia Phillies World Series parade in Philadelphia, PA. There were so many people watching the event on my network that it completely overloaded my 100Mbps Internet link.