Now it's confirmed. Keith Kizer of the NSAC has confirmed that Nick Diaz tested positive for marijuana metabolites, which is the scientific way of saying he had weed in his system. Nick is a known marijuana smoker, and he makes no apologies for it. He'd tested positive once before, in Japan, after beating Takanori Gomi in Pride. His win was overturned and ruled a no contest. In this case, Condit will keep the W, as Nick faces a suspension, fine or both. A complaint for disciplinary action has been filed against Diaz.
This means that not only will we not see GSP vs. Diaz any time soon, it means that the rematch between Condit and Diaz won't take place either, which is another blow to the UFC. They wanted a rematch because they were hoping to make GSP vs. Diaz, a big money fight.
Also, Diaz did say immediately after the Condit fight that he was retiring. People chalked that up to his disappointment with the decision, and didn't really believe he'd never fight again. However, with this failed drug test, he just might hang up the gloves, sending his career up in smoke.
As soon as the NSAC announces the disciplinary action, I will post it here.