It's wise to be wary of ANY person who wants to become a politician. While there are some politicians who practice that trade because of the right reasons, there's yet another reason why Congress' disapproval rating stands at 62% with an approval rating of 31%
Aug. 09 Gallup Poll. - it's called "nobody trusts the bastards in Washington - NONE of them".
All the same, Petraeus is a scholar. He graduated in the top 5% of his class at Hudson High. He has a Ph.D. in International Relations from Princeton. While that isn't a guarantee that he'd be a superior president, it does mean he's got the creds in that department.
He's also a tough bastard. From Wiki - he was shot in the chest in a live fire exercise and made a full recovery. He's a competitive runner and routinely smokes men half his age. Ranger School - distinguished honor grad.
He's a very smart guy. And physically tough.
For those reasons, I think he would want to stay the hell away from politics.