From multiplayerblog.mtv.com:

The next Xbox 360 dashboard update, which will include Facebook, Twitter and Last.FM integration, is going into public beta later this month, according to a Microsoft representative at today's Microsoft Open House event in New York City.

Jennifer Puzio-Brookes, an Entertainment Manager for Xbox, showed off the update in a behind-closed-doors session, and it seemed to include all of the major features promised in Microsoft's E3 press conference. Puzio-Brookes mentioned that a public beta will be released "middle-towards-end of October."
Full Story: multiplayerblog.mtv.com