one thing worth mentioning, if you use nicotine extracted from tobacco, you will have the same nitrosamine/carcinogen situation that we have with the factory made eliquid, the nicotine gum, and the nicotine patch. The levels are lower than that of cigarettes, but they are there. Only reason I mention it is because some might think "make your own and eliminate all of the carcinogens".
And, of course, there's the hazmat thing like VoiceOfChoices posted, which should be taken very seriously due to pure nicotine's toxicity.
edit to add: from my understanding, Johnson Creek has switched to synthetic nicotine. As far as I know, theyre the only eliquid mfg. that uses it.