@Ego: In simple terms, you may have already answered that. Perhaps we experience consciousness the way we do because it's evolutionarily adaptive for life in our world. I started to allude to this: there could exist alien worlds with very different environments, very different forms of life, etc, that would experience consciousness in a completely different way, one that is more adaptive to their particular environment. (I like to use the Tralfamadores from Vonnegut's "Slaughterhouse-Five" as examples:
http://en.wikipedia.org/wiki/Tralfamadore).
In terms of WHAT the purpose is for our experience of consciousness here on Earth, again, I don't have a ready answer; but I can offer that intuitively, it would seem that a rabbit facing a predator and aware of life in terms of "I am master of my own destiny and I need to run away now" has a better survival chance than a rabbit whose awareness is more in terms of "I am nothing more than rabbit-skin, rabbit-bones, and rabbit-brains, all of which are physical matter bound by causal physical chains therefore entailing a predetermined chain of events from the beginning of existence to its end and therefore whether I will escape now is ultimately already decided-- *CHOMP*" (as philoso-rabbit is devoured). The "illusion of choice" seems advantageous in a world structured like ours.
I don't really like this explanation any more than you will, but it does seem intuitive. Beyond that--I like the explanation that the sensation of what we think of as consciousness is simply the qualia (
http://en.wikipedia.org/wiki/Qualia) or "how it feels" to be in corresponding brain states, but I agree this only reveals "how" we feel consciousness and does little to address the "purpose" for feeling consciousness the way we do. (Of course, your argument is also based on the premise that there is a "purpose" for every feature of an organism. I'm no biologist and can't think of any counter-examples--the human appendix sprang to mind, but apparently it served an evolutionary purpose once--so I'm inclined to accept the premise.)
That said, I still disagree that not knowing the purpose of the "illusion of free will" is a serious problem for the theory of determinism. I guess when it comes to unanswerable questions, I'm more comfortable with "what is the evolutionary purpose of the illusion of an efficacious consciousness" than I am with "how could non-physical events like mental states interact in a causally efficacious way with physical events?" It just doesn't fit in with our understanding of causation.
To play Devil's advocate, let's suppose that free will exists and we are able to choose between our actions. Where do you propose that choice is made? Is it a physical event or a non-physical event?
(As far as the problem of evil, it's been a while, but I seem to recall that's something like how does evil exist if God is benevolent? I never understood why that was a problem. The Bible and other faiths seem to have this covered already--God is not always benevolent (see: Sodom and Gomorrah), and/or God creates evil to test mankind.)
@bigato: LOL, I agree with you. Though philosophers prefer the term "thought experiments" to "imagination".

Theoretical understandings do tend to fall apart in practice and are probably annoying to more pragmatic thinkers--could explain why philosophers have something of a history of being fed hemlock. Still, I find it enjoyable to debate, even if human knowledge may never be able to prove or disprove a theoretical understanding.
As far as weather, there are more factors than water evaporation that go into creating weather--wind, atmospheric pressures, a butterfly flapping its wings in China

. Again, I fully agree that humankind may never know all those factors to the extent required for a 100% prediction rate. Then again, maybe we will? Either way, theoretically it holds true that if you did know every causal factor involved you could predict the outcome.
@Chad: What logical fallacy?
I'll probably have to start reading up on theories of consciousness now. Thanks guys, I'm finding this discussion quite stimulating. We should make a philosophy thread. That or I should go drink hemlock.