I have the AJAX working, now just need a measurement by the server of the time between the most recent button press and the incoming request.
Could also use js (or the browser) to measure the time required to ping-pong 100 messages between the two.
Could also try always having an AJAX request open and completing the request when user interaction happens. This way, some of the overhead is already completed before the UI event. (this is called Comet?)
Another interesting test would be to measure throughput.
I just completed another test by embedding gtkmozembed into an application and connecting a load_url to an entry's change event. It is not possible or only slightly possible to detect any delay. This is sending info from app -> local server -> back to app very quickly. Could potentially also use the title bar to get information from the local server to the gtkmozembed and out of there into the app.