Harry Fuecks over at Sitepoint just put up a great article about the different uses of Ajax out in the wild today. He affectionately calls the two categories, HTML++ and Client/SOA. I would suggest reading his article for a better explanation of both. This topic is very relevant to me at the moment because of the project I am currently working on. Quickly explained, I'm working on a team that is building a distributed SOA for wireless clients. Thus bandwidth and latency issues become a HUGE problem. The solution we've come up with is to put a webserver locally on the client machine. Thus, Ajax & HTML are served from localhost. Then, when data is needed, PHP handles fetching and caching locally over the wire.  read more »