My thoughts:
In the end it will be taxed/banned.
Personally I think the most effective tax would be on the manufactures of the liquid nicotine, though they will probably include a tax on hardware as well.
Outright banning or creating a prohibitively high tax will force these products to the black market. Enforcing a ban (either on the product it self or on the blackmarket that results) becomes very costly (War on Dr*gs anyone?) Not just for the cost of the increased police force, prosecution, and jailing of convicted offenders. The blackmarket by nature is not something the government can control.
Given the US is trying its hand at what I consider an approach to socialized medicine, things that provide an unnecessary health risk will need to be over taxed to off set the cost of the impact to the rise in medical visits (though maybe this is an arguement FOR vaping over smoking... healthier alternative and all that).
More than that "logical" approach, people in their cushy tobacco related jobs (Big Tobacco as well as ALA and such) will fight to have tighter regulation.
At the end of the day the politicians generally want to stay in office or move up. That means going with the consensus of their constituents. If a majority of your constituents aren't happy you will likely be voted out next term. This leads to less of a principled approach to governing.
My personal opinion is it should be the adults choice on what they put in their body. If you choose to smoke whatever or drink whatever, that's your choice and you will pay the price. The best approach the government should take is inform instead of trying to "protect us from ourselves." Regulation that goes to improve the quality of a product (within limits of course) isn't always a bad thing, as long as the bar to entry isn't so high that it takes a small fortune to receive/maintain approval. That said, I believe the free market approach we have now is doing a great job of self regulating - anyone with a flashlight body can make a mod, but the market is flooded with competition, so if your battery has a reputation for exploding, chances are you will not be in business long.
Final thought: Our governments (local, state, and federal), by and large, spend more than they bring in (taxes). This means they need to cut overall spending (yeah right) or increase taxes. When they start loosing significant amounts of money in one area, they need to offset that "loss." Vaporizers are a natural target to offset the loss in revenue from traditional tobacco as that is what is replacing the traditional tobacco tax base.
