Amazon entered the CDN business today, as usual Dan Rayburn has the inside scoop. Basically, Amazon will be leveraging its distributed hosting and storage systems for basic CDN services. Not video, yet, and no add-on services, just do-it-yourself caching and download really. But that's enough, if they succeed at all with this offering it will probably annihilate the 40+ small fry that are still seeking a foothold.
Smaller web businesses that need rudimentary or small scale CDN services really seem to have no reason to go elsewhere, upgrading to Akamai et al when they grow larger.
As for the CDNs with their own fiber networks, this shouldn't really affect the situation much. If owning the network gives them some advantages against specialists Limelight and Akamai, those advantages work equally well against an offering from Amazon which is similarly fiber free. And both the CDN specialists and the network based CDNs are really interested mostly in the hopefully taking off video market, which Amazon is not targeting yet.
What I'm wondering though is how much settlement free peering Amazon has. I really don't know the answer, but surely they don't have edge servers of the sort Akamai has. Will they be buying mostly IP transit to deliver their bits?