I know this is probably against the grain, with McCain liking specially-tailored townhall meeting-style debates and all. But I believe Obama should agree to some townhall style debates and not be overly cautious in restricting the crowd that attends.
If the "Obama is a prima donna candidate more comfortable parading before foreign audiences who can't or won't come down to earth to hobnob with the Regular Americans" meme isn't a constant GOP trope yet, I can guarantee it will be as the campaign goes on.
On top of it, Obama needs to be seen getting his hands dirty, as it were, taking risks, campaigning in relatively unfamiliar terrains and before potentially hostile audiences. I fear he's being too careful, in danger of immitating the overly-assured 1948 Dewey campaign whose candidate once wouldn't come out from inside the train to greet voters while Truman spoke out from "whistlestops" all around the country, helping to pull off the come from behind win.