I believe in God and everything, but this is my rebuttal.
My greatest startup:
Will be known by everyone, make me trillions of dollars, solve world ills, and bring sheer beauty to the world.<p>If it doesn't exist, it isn't my greatest startup, is it? Therefore it must exist. Why do I have a day job again?
Heh, like philosophers have never seen this argument before. Granted, it took a while to refute but none other than Immanuel Kant pretty much destroyed the ontological argument a long time ago.<p><a href="http://en.wikipedia.org/wiki/Ontological_argument#Kant:_existence_is_not_a_predicate" rel="nofollow">http://en.wikipedia.org/wiki/Ontological_argument#Kant:_exis...</a>
That's not a proof by any definition of the word I understand. Imagining something does not prove the existence (or otherwise) of that thing.
[edit] but a 10th century bishop writing 77 years after the end of the 10th century is still noteworthy :o)