I am, at this point, a genuinely undecided voter. I have no clue who I'll pull the lever for in 2008 (though I'm comforted by the fact that my lever-pulling will have absolutely no effect on my party's nominee). But if I were going to decide on Obama, this is exactly why. Insofar as there's a real hope for a new foreign policy, I think it lies with Obama. That's not to say Edwards' policies on this are bad, but what moves him is, as far as I can tell, economic injustice at home, so I think his foreign policy would be a bit secondary. And Hillary Clinton's policies would, as far as I can tell, be bad, at least as compared to the other two.
It's also worth remembering, when you think about foreign policy and the Democrats, that the president has considerably more autonomy on foreign affairs than s/he does on domestic policy, where the executive is hemmed in by Congress, the filibuster, etc. There's a case to be made that given their relative nearness in domestic policies, that you should go with whomever you think would do the best job abroad. I'm not sure I agree with that argument -- particularly because health care reform will take some real skill -- but it's one I'm wrestling with.
