Kaspersky posted up a video discussion about Stuxnet at: Lab Matters Webcast: Unraveling Stuxnet. High-lights to me are that they state that parts of Stuxnet show it was compiled in January 2009, and the expert being interviewed, Roel Schouwenberg, says that development and planning must have begun in 2008, and was probably done by a team of 5-10 top experts, and additionally lots of testing had to have been performed on it. Because of this, and because it's purpose is sabotage and not espionage, he claims Stuxnet had to have been backed by a nation state. Also, he notes that Stuxnet had 4 0-day exploits for Windows, and that just having one 0-day is big news for any malware, and 2 is unprecedented, so 4 again hints at top experts being behind it.