Reviewers and users often commend Apple for its attention to detail. From Mac OS X to the MacBook Air, Apple engineers seem to spend significant resources polishing things to a mirror shine. So, when buying a $2,800 Mac Pro, you wouldn't exactly expect the machine to choke you in potentially cancer-inducing gases.
According to the Guardian, however, that may be just what some folks are getting. Quoting a story from French paper Libération, the British paper says Mac Pros emit a burnt plastic odor caused partly by benzene fumes. A molecular biologist uncovered the issue and has gotten the attention of both Greenpeace and France's national institute for environmental and industrial risks. Benzene fumes could cause sensitive users to develop leukemias after just two months of daily exposure, says Annie Leszkowicz of the French workplace and environmental safety agency.
On the upside, you might notice the problem before you get cancer: the Guardian has spotted two separate reports of users complaining about the odor's conspicuousness. This user on the MacRumors forums says the smell is "intense, nauseating, and makes you feel funny," while another Mac Pro owner on the official Apple support forums says, "I recently purchased the new 8-core and it emits a very musty odor when powered up. My entire room soon smells bad and I have had to resort to a few air fresheners just to be able to work on it."
Update: An Apple spokesman has told MacWorld, "We have not found anything that supports this claim, but continue to investigate it for the customer."