The source may have come from right field, but I have a very hard time swallowing the idea that Obama authored such a well written book when he had absolutely zero prior written materials that even hinted at the talent level displayed in the book.
It may not have been Ayers, but someone else wrote that book, imho, and that fits in with the rest of Obama's slickly manufactured image. To an extent it happens with all of the candidates, but Obama has become a cult of personality type figure whose myth has far exceeded his record. I think the book is likely another example of creation of Barack Obama the New Messiah.