Pretty impressive work. I personally use nicotine gum (as does President Obama, a health nut) as I'm allergic to caffeine. I have used melatonin in the past, though given this I will use it more now.

The key I find is to only use them when you have already outlined in a detailed way a significant set of tasks that need to be performed or a particularly critical meeting where you already have a very strong background.

For learning, general creative process I don't use them.

The biggest problem is managing the physical addiction (ie, you feel very tired) when you're not taking them.

Also there is some evidence that nicotine increases incidence of cancer. Not to mention what it does to my blood pressure, though I find constant exercise helps manage that.