On one hand, I could see the Master covering all of his ground. On the other hand, the title of the books and the 'Potions of Life' made it a bit too hocus-pocus for me. XD

I didn't mind the whole Obama thing since we have Queen Elizabeth the Second and other people in the past... but that's just me. I thought it was used to show that the episode was taking place here and now in 2009 and to show that the best way was to have Obama in it since he is here and now.