Romney and Pawlenty have made comments indicating they are not it. Sarah Palin has allegedly been seen getting on a plane overnight with her kids.
Palin's credentials are there. She is an energetic reformer who took on the corrupt Alaska Republican machine and won.
Palin would be a risky choice. The base goes wild, but McCain has the base already (let's not kid ourselves; myself aside, conservatives will overwhelmingly vote for McCain). It may pay off with women and Hillary supporters, but that's questionable. If she's portrayed as a right-wing anti-abortion candidate, the pick will backfire.
Still, the risks are worth the likely upside. It's the anti-Biden pick. Obama went safe and got a dud; McCain took a chance and may have caught a star.
UPDATE: Holy crap. Look at Palin's bio. Moose hunter, beauty queen, pilot, musician, ice fisher, marathon runner.... She makes Chuck Norris look like a sissy.