before everyone gets on their high horse lets put this into perspective. Numerous 'studies' have been done - as a previous poster has said, no mention of concentrations, type of release etc etc. As these people obviously have an axe to grind i would assume that if any real scientific evidence of a problem were found then they would be publishing it far an wide. The silence on the hard data speaks volumes really.
Also one of the most vocal proponents of this problem that I used to work with smoked 40 a day, however was quite happy to keep trying to bash the company about this issue! This was clearly more of a political issue for him than a health issue.
Also how about some relative data - what is the air quality like sat in a traffic jam on the M25, or in a totally sealed airconditioned office (where most of the rest of the population work) eh? I bet there are equivelent risks everywhere.
I recently spent a week in a central asain city and came home with a cracking headache, and bad throat / runny nose etc. Bad cabin air? Nope - horrific polution and traffic fumes in the city. I know which parts of my job I'm more worried about and where I feel my health is most at risk - and it aint on the flight deck!