I haven't read most of the posts before me in this thread (there's six pages of them, give me a break), so I hope I'm not just repeating things that were said earlier.
As far as free will goes, I don't think that pre-determinism really affects it at all as long as people aren't told of what is going to happen. Calvinists say that from before each person is born, God already knows whether they will go to heaven or to hell. If people actually knew whether they would or not, this would affect things, but they don't know. All they know is that God knows. So for those who just assume that it was pre-determined that they would go to heaven and therefore don't try to be a good person, it was probably already known that they would think this way and act accordingly. Therefore, it's likely that these people were pre-determined to go to hell. From the other perspective, if someone acted well their whole life, despite the fact that they "knew" they were going to go to heaven, it was probably know that they would act this way too, and it was pre-determined to go to heaven. It only gets messy if somebody on Earth knows who is and isn't going to hell (unless this knowledge is ever-changing based on the effect of telling people about their fate).
But what makes this more interesting to me is if we assume that God isn't omnipotent. What's always made little sense to many people is why God is said to only create good, and only advocate good, and yet he doesn't get rid of all evil on the Earth. (This is interesting to me as an atheist because Christianity and Islam are the only two religions that have these notions of absolute evil. But obviously, the idea is very popular, as these two religions are the most popular ever made.)
But assuming that there is a conflict in the fact that God did not abolish evil, contemplate this: Suppose that you are God. You have existed from the beginning of the universe, know everything that's ever happened and everything that ever will happen, but cannot directly affect the world. One day, you find that you have a spontaneous connection with someone on Earth, let's call him Joshua Christ. What would you say? I mean, if God did exist, and he was going to put one person in charge of transforming the world according to what was best for humanity, the only reason of why he would do this that seems likely to me is because he didn't have the power to go down there and do it himself.
If I've offended anyone with this, just ignore me and I'm sorry. I know that religion can be a very touchy subject.
-giusti