1. A content delivery method operative at a server to which a client machine has been directed by a content delivery network (CDN) request routing mechanism, the server having a cache, wherein the server is managed by a service provider and shared by a set of participating content providers that provide content to be delivered over the CDN, the content delivery method comprising: upon receipt of a request for given content from the client machine that cannot be serviced at the server, fetching the given content from an origin server; determining whether the given content should be stored in the cache in an uncompressed or compressed form by evaluating a function trading off anticipated storage time in the cache versus processing overhead required to perform the compression; selectively storing the given content either uncompressed or compressed based on the determination, wherein the determination overrides a control for the compression routine that would otherwise apply.