What Experience is Obama Lacking?

[Jophiel]

Ever since, well, since Obama spoke at the DNC and people started saying he'd be president someday, I've also heard "He's not experienced enough". But I haven't heard anyone explain exactly what experience he's lacking, particularly when compared with previous presidents.

As I understand it, Barack Obama spent a decade teaching constitutional law, so I'd think he knows his American governmental system on paper. He spent eight years in the Illinois State Senate and a couple years now in the US Senate so he has legislative experience. He's been on the Senate Foreign Relations Committee so he has at least dipped his fingers in the international relations pool.

I guess I'm just wondering what qualifications did Bush/Bush Sr, Clinton, Reagan, etc bring which are essential for "having the experience" to be president? A governorship? Is it the experience with working a state budget? Experience with working with a legislature? If so, would it matter how many Senate terms Obama served? No one is hassling McCain about his lack of executive experience as a governor, mayor, etc.

I don't have a horse in this race yet. The election is forever away and any number of people may join, drop out, etc. I'm just asking about the basis for the "Not enough experience" criticism for Obama.