Obama has never submitted conclusive evidence that he was born in the United States. What he posted on his website is a document called Certification of Live Birth, laser printed from a computer in 2007 regarding a document filed four days after Obama was born. It is not a Certificate of Live Birth, which at the time, would have been typed and signed by the doctor on the day the child was born.
There is a significant difference between the two documents. Read
http://peoplespassions.org/documents/birth_certificate.htm for an explanation.
The arguments being made against his being born in the US center around one scenario. Under Florida law at the time, a foreign born child's parent could bring the child back to the US after his birth on August 4, 1961, and file a Certification of Live Birth form on August 8, declaring with scant proof that he was born in the US. This Certification of Live Birth contains none of the traceable documentation, like doctor's signature on the day of birth, etc., found on a Certificate of Live Birth, which is why people want to see his Certificate of Live Birth. It only seems reasonable to require that a man who is elected the highest office in the land, prove by clear and convincing evidence that he meets the US Constitution's "natural born citizen" requirement to become president.
For those of you who do not think this issue is a big deal, then let's see you accept secondary evidence of domain ownership or payment the next time you buy or sell a valuable domain. If the best evidence is out there, then by god someone ought to produce it.