A third of the world. (2 billion Christians)
Actually, most of that isn't because they chose to love God, it's that they don't want to choose the possible alternative. I bet you if there was a third choice, people would opt for it. In christianity, it's love god or be tortured in hell forever. Not exactly fair, is it? Using scare tactics to influence a person's choice is the bare minimum of what you can call free will. Yes, they have the choice to not accept god, but if they do, they are tormented for all eternity. Therefore, they'd choose god, just to escape Hell. There's really nothing genuine in that.
Again, my parent/child analogy works for the "curiosity killed the cat" thing as well. If the cat goes out searching for trouble, then it gets what it deserves, but if trouble was placed right in front of it, then the cat shouldn't be held totally responsible.