1. A method operable in at least one content server for delivering content to a client over a computer network, the at least one content server having at least one processor and memory holding instructions for execution by the at least one processor, the method comprising: receiving a request for web content from a particular client device; determining that the particular client device has characteristics that match one of a plurality of sets of stored characteristics for client devices, each of said plurality of sets of stored characteristics being associated with one of a plurality of versions of said web content; obtaining the version of the web content that is associated with the matching set of stored characteristics; serving the obtained version of the web content to the particular client device, in response to the request for web content.