GBRK,
I believe that our salvation is not "complete" until we leave this earth. Every second, every action before that time counts.
I believe that we can turn away from God. We could say our Salvation prayer, or whatever it is called (with all due respect, please- i just don't know it" and accept Jesus as our Saviour. But then we could, years down the road, reject Him. We could fall from grace- in sin, in our hearts, in our compassion, etc.
My best example is this; Like He says "Depart from me, I never knew you", to people who had been sharing His Word, and devoted their lives to Him.
I consider that above quote to be evidence that God does in fact refuse salvation to a presumed Christian.
Hope that answers your question.