The science is not in

From an editorial in today's USA Today by Jacob Sullum:

Surgeon General Richard Carmona says secondhand smoke is a deadly public health hazard, lending support to government bans on smoking in private businesses. Surgeons general have been saying the same thing for two decades, but that doesn't make it right. The dangers posed by secondhand smoke are debatable and likely to remain so given the limitations of epidemiology. It's well established that tobacco smoke can raise the risk of diseases such as lung cancer and heart disease. The question is how much it takes.