According to the info on the apple site about Keynote and its features, there is an option when projecting from a digital projector, or when you have a second screen attached, to present the show on the second screen.
I am assuming that it will then present the slideshow on the second screen, leaving the primary screen free to do other stuff. I hope it is possible to work on the screen on the fly while having the presentation on the second screen. This would be very useful for me.
Cant wait to try it though. Especially as trying to work with dynamic text and embedded music and QT movies is not that impressive in PPT. Now, if only I was one of the lucky 85 million within 15 miles of an Apple Store!!
Andrew