Engadget reports that the fall update has just been made available to those in the preview program:
Shortly before Kinect hits store shelves on November 4th, Microsoft plans on rolling out the Fall Update to Xbox Live — even sooner for those who signed up for the preview program. That shouldn’t come as much of a surprise, really: even without the numerous leaks, the fall update is a longstanding tradition for the almost five-year-old console, and the company devoted a large chunk of its E3 2010 presentation to talk about the biggest additions. That includes Netflix search (finally!), Zune music, and an entertainment hub for a certain worldwide sports broadcaster… ESPN.
More details available in their News item. What you won’t find in there is that the new Xbox experience is finally Windows Live Messenger MPOP enabled. A source close to LiveSide just revealed this.