Hey Brian Sloan aka Bzrd.
I noticed you started posting regularly again but didn't post right away because i've brain pretty occupied lately. At any rate, it's good to see u back (with some philosophical ammunition no less).
In philosophy, we apply the term immaterial to entities which are not located in physical space - this doesn't apply to thought because if thought is something material, it does exist in physical space, namely in the brain. Therefore, not being able to directly observe something is not a criterion for labelling something immaterial. For instance, we can't directly observe causation (we can only indirectly infer it), but that doesn't make causation immaterial.
So what i'm driving at is thought is not immaterial... i'm inclined to believe it's a consequence of physical phenomena happening in the brain. We can debate it as much as you like, but physical evidence seems to suggest that we can effect thought by introducing various chemicals or neurotransmitters to the brain. Hallucinogens can impair cognitive function to the extent where the agent seemingly experiences a completely different reality. I don't think we can deny that thought certainly has SOME physical basis.
Of course i can see where you're coming from with the "immaterial-thought" hypothesis. Thought is intangible and often seems to arise out of nowhere. This to many, suggests the possibility of the supernatural, and i'll admit, it's a profound and difficult question. I used to think to myself "can pull out a bunch of neurons from my brain and actually hold abstract concepts and ideas in my hand?" It's a weird thought.
However, something like a "soul" would be considered immaterial. The contraversy lies in the problem of how an immaterial entity could effect the material world. How does something that exists outside of physical space produce events within space?
Furthermore, no sources of information point to the existence of a soul. If a soul is something immaterial that exists over and above physical and psychological states, we have no clue of knowing if it exists. Consulting our senses, physical experience, or introspection can only give us information about our physical and psychological states - we have no means of accessing any part of us that may be immaterial. We can however, access our thoughts... which to me supports the idea that thought is indeed a material thing.
Not that we'll find an answer to this problem any time in the near future - science just isn't equiped to deal with these sorts of questions. It IS rather humbling to consider how little we actually understand about the world though...