The Ontological Argument for the Existence of God

[Ravenshire]

I have never seen this argument before, so I'm interested in some discussion of it. A philosopher by the name of Alvin Plantinga states it this way:

The Ontological Argument

1. It is possible that a maximally great being exists.
   
2. If it is possible that a maximally great being exists, then a maximally great being exists is some possible world.
   
3. If a maximally great being exists in some possible world, then it exists in every possible world.
   
4. If a maximally great being exists in every possible world, then it exists in the actual world.
   
5. If a maximally great being exists in the actual world, then a maximally great being exists.
   
6. Therefore, a maximally great being exists.
   

Thoughts?

Every time I see a christer bring up an argument "proving" his particular gawd that starts with "It is possible..." I think of this:

Christer: It is possible that a maximally great being exists.

Me: Well, I guess, maybe. But, it's an insanly small chance.

Christer: