1. A method for tracking abandonment rates, comprising: a client computer sending a first message to a server computer, the first message requesting a content unit to be incorporated into a web page the client computer receiving, from the server computer, the content unit including deliverable content and a communications element configured to send messages generated by the content unit to the server the client computer delivering the deliverable content after delivering the deliverable content, the client computer sending a second message to the server via the communications element, the second message indicating that the delivery of the deliverable content has been completed.