From Mike Allen at Politico:

Retired Gen. Colin Powell, once considered a potential running mate for Sen. John McCain (R-Ariz.), now may endorse his opponent, Sen. Barack Obama (D-Ill.), according to Republican sources. But an air of mystery surrounds Powell's planned live appearance Sunday on NBC's "Meet the Press," and no one is sure what he will say.

First, this may just be hype to increase ratings for the "Meet the Press." Second, Colin Powell? Is anyone still paying attention to him other than a few obsessive political junkies (cough)? I think that he would have been helpful early in the campaign; Obama could have used his endorsement to back up his military/foreign policy creds. But the debates are done. It's all over but the ad blitzes. The only way a Powell endorsement would significantly affect the race, IMHO, would be if he offers such full-throated praise of Obama and condemnation of McCain that it echoes across the nation's headlines, causing Joe Undecided to murmur with surprise over his morning coffee. But I don't think that's Powell's style. Still, I welcome a Powell endorsement even if wouldn't make much difference. It would nonetheless be a great thumb in the eye(s) of Bush-McCain.

Late update: He did endorse. It was eloquent and quite damning of McCain but not IMO soundbitable enough to make Joe Undecided murmur over his coffee. I also note that he said that he will not campaign for Obama. I do commend the endorsement though. Powell's defense of religious tolerance is particularly admirable and eloquent. I wish that this had been said more often by people of his stature. Here's the video.

And here's a Q&A with reporters afterward: