quote: What is consciousness supposed to be doing, exactly? If we're abandoning the concept of a spirit, or a soul, then there is no mechanism whereby your consciousness decides something and influences the physical processes which produce your behaviour.
I think you're confusing yourself here by assuming that there SHOULD be a clear distinction between the two. If physicalism is true, then the mind - including consciousness - is simply a different view of those processes - it's how it looks to us. (And dualism doesn't actually offer a mechanism for the mind to actually interact with the body at all - that's one of it's weaknesses).
quote: Your behaviour and, presumably, your consciousness, is produced by deterministic physcal processes in your brain - it does not direct these processes.
Think of it from the point of view I'm giving you. Some processes can direct the outcome of other processes, so on that view there certainly can be direction. (And again dualism doesn't have anything better to offer. A "spirit" or "soul" still has to operate in some way).
Indeed, we can ignore the whole question of physicalism versus dualism to deal with the concept of libertarian free will.
Either the sum of external circumstances (external to the mind), your current mental state and the nature of your mind are sufficient to dictate your decision or it is not.
In the first case then we have determinism, in the second we merely have a random element, which is not a part of your current mental state or the nature of your mind (the presence of a random element might be, but it's effect on your decision making is not).
Neither gives us meaningful libertarian free will. Indeed, determinism seems to be the least bad option. For we cannot be responsible for a random element within our minds.