My current thinking on the subject is that consciousness is not what we think it is. I think the phenomenon evolved probably because it proved useful for our ancestors to know which actions were caused by us and which were caused by others. But, I think we are given the sensation that we have decided to do something after our neurons have already computed and sent the signal to commit the act. (see Libet's famous experiments: http://www.consciousentities.com/libet.htm).
I do not think we are really able to make parts of our brain functioning available for review. Several tightly controlled experiments have shown that we often have no idea why we do what we do or have the thoughts occur to us that we do, but if asked why we gave the answer we gave or did what we did, we will make up some plausible explanation out of what is available to us and firmly believe that our made up reason is the real reason why we did what we did. This is the same process that goes on when we speculate about the reasons for the actions of others. We are observers of our own behavior and then speculate as to the reasons why; we do not appear to be able to actually review the real antecedents.
For a nice, light treatment of the subject that I think most will enjoy (probably not dcleve), read this: http://www.susanblackmore.co.uk/Lectures/Tampere%202005.htm