A nit, we actually know very little about nicotine since most of the studies are about tobacco use. Further, it's almost impossible to find subjects who use(d) nicotine but not tobacco. However, Sweden has a large percentage of people who use snus with little ill effect, and is one of the better sources of data on purer nicotine (but snus is still tobacco, just a purer form).

Also, we know that inhaling smoke is bad and that tobacco smoke is bad, but we don't know about hot vapor so much, let alone hot nicotine vapor. There is more research needed here and I look forward to it. It's pretty safe to assume though that it's safer than cigarettes.