I am getting more questions in the office about Open Space Technology. There are quite a lot of information on the web — once you know were to find it.
I find this one a useful introduction. Though it describes how a past conference was to be organized, it does summarize quite well what the basic principles are.
This page lists a few short stories regarding the outcome of a Open Space conference. Quite fascinating.
It should also be noted that Open Space will be used in a part of Agile 2007, as it has been the case in previous editions of the conference.