What should NOT factor into his decision is the gender, ethnicity, sexual orientation or religious background of the Supreme Court nominee. Granted, I haven't really heard from anyone calling for a Mormon justice or a gay justice (although I'm sure if I conversed in the proper circles I would) but every day when I open up the newspaper there's an opinion column or a letter to the editor calling for a Latino justice, a woman justice, an African-American justice, etc. GIVE ME A BREAK! If the best person for the job does turn out to be a Latino Woman whose parents were illegal immigrants, then so be it. Nominate her. But don't nominate her BECAUSE she's Latino or BECAUSE she's a woman - nominate her because of her experience, past decisions in a courtroom, etc. If Obama ends up nominating another old white guy because he feels that man's experience will best balance the court's decision-making, then so be it. Don't scream foul because he wasn't a woman and he wasn't a minority.
(Also, side note - Asian-Americans, why aren't you campaigning for an Asian-American justice? I just realized I don't think I've heard a peep proclaiming why the repressed Asian-American needs a voice on the Supreme Court.)