If the deal goes through, it may require Facebook to take a different approach with their CDN strategy. They will probably either begin to roll their own (given their size and budgets), or move to a blended environment where they utilize multiple CDNs based on region and traffic levels.

For example, Apple historically has used Akamai for their content delivery, but as of around ~2009, they began to use Limelight in conjunction with Akamai. Just today with the iOS 5/OS X updates, I noticed at home in Los Angeles that the delivery from Limelight was terrible. I tried it again about an hour after release, and I was then being sent to Level3.

Suffice to say, Apple is now using three CDNs.