Dynamic documents are easy to use, and have been used to do some really amazing stuff.
A client pull allows the server to tell the browser to load a certain document in a certain number of seconds. This document will reload itself once every second. Some sites use this type of client pull to refresh a document such as stock quotes or a video camera pointed at a city street. Client pulls can also load a different document in a predefined number of seconds. This example will send you to KSU's home page in 5 seconds.