Executive experience is defined as having run a state or a business, right?
A presidential campaign is a business, you know. A business of which the candidate, namely Obama or McCain, is the CEO. They're big businesses with departments for communications/speechwriting, advertising, policy, scheduling, fundraising, etc etc. Each of the departments has a director, usually chosen and appointed by the candidate him/herself. Decisions are made every day, and the biggest/most important ones are no doubt made by the head honcho - the candidate. It's a business and the candidate - Obama or McCain - is running the whole show, has the final say on everything and bears the ultimate responsibility and/or blame for everything.
Considering that this business of Obama's has raised anywhere from 265 to 340 million dollars so far this election cycle(aka since its foundation) and has in the neighborhood of 60 to 70 million dollars on hand right now, and considering it managed to fill a stadium with 84,000 people the other night to support it, and since it has the support of probably 55-60 million people nationwide, and since he has been complimented by many for how well he's run his campaign, I'd say he's doing a hell of a job running this business of his, and since this business will be nearly two years old when all is said and done, I'd say that's some valuable executive experience.
And I don't know the exact numbers for McCain, but if he's still here, I guess he's doing an ok job(though not as good as Obama) running his business too.