The Constitution is no where near authoratative on citizenship issues. How could it be really?
Its not like guys like George Washington and John Adams were born in the USA (the USA didn't exist, they were British citizens) and they were still president. The founders knew that when they wrote the Constitution, so the wording was intentionally made vague. Obama is the son of a British man, just like the founding fathers were.
Like it or not, Obama was born in the USA. Even if he had retained Kenyan (British) citizenship, at worst he would be a citizen of two nations. I'm in London at the moment, and there are numerous professors here who are American and who maintain dual-citizenship (although you can only vote in one country).
Jackson is right too - since the President nominates Supreme Court justices there is really no way to enforce whatever citizenship qualms people have with Mccain or Obama since the justices will want appointees on their 'side', and it would reek of political preferences in the wake of the 2000 election when the Supreme Court decided essentially that recounts were unconstitutional.
People are difficult to govern because they have too much knowledge.
When there are more laws, there are more criminals.
- Lao Tzu
