It was reported in Esquire that everyone on Jon Huntsman's campaign has been asked to call him "Governor", "because governors become Presidents". In total, seventeen U.S. Presidents have been former Governors.
Governors have had executive experience, and voters may think that if you can lead a state, you can lead a country. Holding the position of Governor is similar to being President - they are rather like Presidents of their own states after all. On the other hand, Sarah Palin is frequently accused of being too inexperienced, despite having been Governor of Alaska, and Barack Obama had only been a Senator for one term before being inaugurated as President.
Apart from New Hampshire and Vermont, states hold gubernatorial elections every four years. This is one advantage over Congressmen (although not over Senators), who are only secure for two years, because it guarantees that Governors will be politically relevant for longer periods of time. It will help greatly that the candidate is well-known, having enjoyed a relatively high profile thanks to media attention over some years. There are only 50 state governors, easier for the common voter to remember than 100 Senators or 435 Congressmen. But, again, Obama defied this presumption by being relatively unknown when he won his candidacy.
Nevertheless, if a Governor is running for Presidency a voter will have a better idea of which policies they'd implement, where they position themselves on the political spectrum and, perhaps, their capability in a crisis. All these are far more applicable to former Governors than Senators for example, who are merely legislators tucked away in their ivory towers.