WSJ: "But in a nation in which 66% of the voting-age population is overweight and 32% is obese, could Sen. Obama's skinniness be a liability? Despite his visits to waffle houses, ice-cream parlors and greasy-spoon diners around the country, his slim physique just might have some Americans wondering whether he is truly like them." Obama's also taller than average, which is well-known to be a disadvantage in presidential politics.
In all seriousness, if the predominant aspect of superficial physical appearance that voters have in their head is anything other than race, I think Obama should consider himself lucky. America can handle a skinny president.