Generally speaking, humans are predisposed to believing in Dualism. To put it briefly, Dualism is the theory that at least some mental processes are non-physical. It's easy to see why we'd think this. It's hard to grasp the concept of the mind and how we think.
The Dualism theory begins to lose credibility when you examine cases where the brain is damaged or altered. There have been many instance where someone takes a blow to the head and has loss of mental function. It is pretty clear that decision making and other brain functions are the result of neurons firing or not firing.
Neural Networks could really be its own fascinating subject, but I'll try to review it quickly here (I'm not an expert, however). Basically, your brain is a collection of neurons that make up many paths through your brain. Sensory inputs trigger these neurons to fire, which in turn triggers the next neuron to fire (if the strength of the previous neuron is large enough). The more a certain path of neurons is used, the easier it is for that path to fire. This is how motor skills are developed, as well as how other skills are learned. Of course it's really much more complicated, but that's the general theory. Some AI systems are modeled this way. It's surprising to see how similarly we operate when compared with computers.
Now I sort of want to switch topics to Randomness. I'll start with a favorite quote of mine:
"Occurrences in this domain are beyond the reach of exact prediction because of the variety of factors in operation, not because of any lack of order in nature."
What Einstein is basically saying here (and what I am inclined to believe) is that there really is no such thing as random. Events happen as a reaction to some prior event. It's as simple as that. We perceive things as random when something happens we do not expect, or when we can't see the pattern. Just like how there is no true randomness in computers, there is no true randomness in nature. I assert that if you knew every variable in operation, you could predict any future event.
You might say, "what about human influence?" Well humans are just another variable in the equation, with brains made of matter that are subject to the same laws of cause and effect. The human brain is a function, with inputs and outputs. It's a complicated function, and one that changes constantly, but it is predictable.
Now what does all this have to do with Free Will? Well if minds are subject to the physical laws of matter and there really is no such thing as randomness in nature, what are we left with? Predestination comes to mind, although I hate the sound of the word. I'm saying that since the mind is simply a function with inputs and outputs, we never actually make a choice. The choice is already made what we're eating for lunch tomorrow. I think we don't realize it because we are not aware of all the processes going on in our brain.
So what does this mean for life as we know it? Nothing really... We will always feel like we're making the choices. I also doubt we will ever have the technology or the intelligence to accurately predict future events (I'm not talking about trivial things like predicting an eclipse).
There are some issues I haven't covered yet in regards to this theory of mine. Humans are self-aware and have the ability to imagine possible outcomes and weigh them. Self-awareness is the tricky one. Why exactly are we aware of our thought processes is unknown to me. My best guess would be that it is a side effect of our ability to imagine.
Imagination is undoubtedly a major strength in terms of survivability. We can imagine possible outcomes based on previous information stored in our memory (memory is located in a physical part of our brain). Using this information we can weigh outcomes and make what we perceive to be a choice. However, these presented outcomes are the output of some process in the brain. The imagined outcomes then become the inputs to our "decision making" function. No choice is actually made however, because the decision making function has a predetermined output based on our imagined input.
So maybe our "thoughts" are just an interpretation of the inner imagination process going on in our brains. Just like the visual system makes an interpretation of the physical world that's useful to us in terms of survivability. (Did you know that objects we can see are mostly empty space? Since we can't actually pass through these objects we perceive them as solid).
So, there are my thoughts on Free Will. Hopefully I didn't ramble too much. I welcome your questions and comments. An opinion is worthless until someone has tried to prove it wrong.