Event driven programming takes advantage of the fact that network servers spend most of their time waiting for I/O operations to complete. Operations against in-memory data are incredibly fast, but anything that involves talking to the filesystem or over a network inevitably involves waiting around for a response.

This is a great summary of the up-and-coming event-driven approach to a webserver (in this case, “Node”). I’ve been doing a ton of jquery/ajax stuff lately and I can say from experience we need support like this on the server-side.