I recently submitted my DNA so that I could be considered for Alzheimer's studies and I got one back that is studying whether or not nicotine would be useful in improving memory functionality. I have a college buddy who is the Chief Science Officer for a major medical research foundation and he has used nicotine for years in order to improve his ability to focus for long periods of time. He did warn that nicotine is one of the most addictive substances known, but he doesn't care - he just stays addicted. He uses gum and patches for his fixes.

I am not worried about Alzheimer's as much as I just want to be able to to top level work in my field (computing) and I figure I only have a few years left (I am 67) and I would like to extend it or make it as productive as possible. I am in excellent health so I probably won't jeopardize that for this gain, but I find the question intriguing.