This is a question that has been hoovering around Obama since the start of the campaign. It gained new traction following Senator Obama's remarks to "Joe the Plumber." So is he?
I doubt Obama is a socialist in the traditional Marxist nationalizations context. Granted, President Bush, by effectively nationalizing the banks, insurance and automobile industries has got the ball rolling should President Obama consider further nationalizations.
Rather, Obama strikes me as a "managerial state" type. James Burnham developed the concept, which has become mostly popular in "paleoconservative" circles as a criticism of modern society. (Of course, the positive spin you could place on Obama's beliefs could be that he is a "Galbraitian" and a believer in the idea of a "new class" to guide society.) I am no paleo, but I think the concept holds some validity.
I think an Obama administration will be very interventionist and regulatory, i.e., very "managing" but not instituting direct state ownership or control. Is there a difference? To some extent yes. But I worry that it will stifle innovation and increase our reliance on the state.