Well, he's not OK for the Presidency, citizenship-wise, even if he was born in Hawaii. Because his father was a Kenyan citizen and not an American citizen, Obama isn't a 'natural born citizen'.
To be eligible to serve as the President of the United States, the person must be a 'natural born citizen' (or a citizen at the time of the adoption of the constitution) per Article 2 Section 1 of the US Constitution. http://www.law.cornell.edu/constitution/constitution.articleii.html
EVERY President has been a natural born citizen (born on US soil to two US citizen parents), or a citizen at the time the constitution was adopted.
A regular 'citizen' of the US is a citizen at birth by being born on US soil (Jus soli) or by being born to one or two US citizen parents (Jus sanguinis).US citizenship can be acquired by naturalization by a non-citizen after birth.
http://www.state.gov/documents/organization/86755.pdf
A US 'natural born citizen' is a person born on US soil to two US citizen parents.
See PERKINS V. ELG - http://caselaw.lp.findlaw.com/scripts/getcase.pl?court=US&vol=307&invol=325
The Supreme Court case of PERKINS v. ELG defined a natural born citizen as a person who was born on US soil to two US citizen parents. It was also defined the same way in MINOR v. HAPPERSETT http://caselaw.lp.findlaw.com/scripts/getcase.pl?court=US&vol=88&invol=162
Mr. Barack H. Obama II was born to a US citizen mother and a Kenyan citizen father and was reportedly born on US soil in the state of Hawaii. He is a 'citizen'. BUT - Since one of his parents was not a US citizen, Obama is not a 'natural-born citizen' and is therefore not qualified for the office of President of the United States.