Well, back in July, Wired quoted Manning as saying

“Everywhere there’s a U.S. post, there’s a diplomatic scandal that will be revealed,” Manning wrote. “It’s open diplomacy. World-wide anarchy in CSV format. It’s Climategate with a global scope, and breathtaking depth. It’s beautiful, and horrifying.”

The article also says "a previously unreported breach consisting of 260,000 classified U.S. diplomatic cables that Manning described as exposing “almost criminal political back dealings.”" ( http://www.wired.com/threatlevel/2010/06/leak/ )

I think it's real, and I think it's bad. Time will tell though.