I thought this was interesting and a good read. Notice that the McCain camp turned down the offer to speak with Nature. I cross-posted this in GDP.
Barack Obama accepted Nature's invitation to answer 18 science-related questions in writing; John McCain's campaign declined. Obama's answers to many of the questions are printed here; answers to additional questions (on topics including biosecurity, the nuclear weapons laboratories and US participation in international projects) can be found at
http://www.nature.com/uselection. Wherever possible, Nature has noted what McCain has said at other times on these topics.
http://www.nature.com/news/2008/080903/full/455446a.html