One of the other posters has suggested that the argument can be used to imply the existence of any conceivable thing, but this is false. Consider, for example, the magic pen that they suggest. What makes it the best possible pen, exactly? Would the best possible pen have infinite ink? Would it write the best stories without any effort on the writers part? Would it write stories without even having to be held? Would it be sentient? Would it be all knowing? If you try to Think of the best possible pen, you can always think of one which is better. Until, eventually, you arrive at an all powerful, all knowing, all good, sentient pen which can change its form if desired and only appear to those it seems fit etc etc etc. in other words, you get God, choosing to take the form of a pen. Yet, if the pen was all powerful and all knowing and all good, and capable of taking any form, the question remains why it should stay a pen. And, clearly, we can see there is no reason at all. Thus, the greatest possible pen would cease to be a pen. And what we are left with is God. Consider what makes a thing the greatest it can be, and you will always return to the concept of God.
If there is a Flying Spaghetti Monster in a possible world then he is possible. If there is a Magic Pen in a possible world then it is possible. This argument is ridiculous and has been refuted. It can be used for anything, there's no reason why an Almighty God is more logically possible than a Flying Spaghetti Monster or a Magic Pen.
Just because an idea is logically consistent with the world as we know it does not mean that it is true. Time and time again, the one has been misappropriated for the other. The various philosophers at different times have always worked from assumptions that guarantee that certain constructs of the mind are reflected in the world. There is no reason this should be the case, or that those constructs would correspond to god if it were. Also, all forms of the ontological argument give such a vague definition of god that I would hardly use it as a basis on which to claim the existence of the Abrahamic god or any other particular god, more of a metaphysical entity with great power or essential goodness. These properties are not exclusive to the Abrahamic religions. Much more detail would be needed before any kind of ontological argument could prove the existence of a god with any specific properties.