I just learned about Convergence 08, a two-day event at the Computer History Museum in Mountain View, CA featuring a bunch of futurists and other thinkers on technology. From their buzzword-heavy blurb:
The speaker list includes some heavyweight futurists/technologists like Paul Saffo, Aubrey de Grey and Peter Norvig, and at least one critic, Denise Caruso.
I'm not sure I get the idea of an "unconference" as the main event, though. I thought those were typically free, alternative forums that took place outside big conferences.