The Ontological Argument - valid or debunked?

[madog]

 
The argument can be summed up as: If you think that it is broadly logically possible that God (the maximally great being most think of when you say God) exists then he does exist.
 

Without man there would be no one to think .... So surely it follows that there can be no God without man .... The rest falls away if he can only exist if man exists and thinks him up ....