Chalk up the first bad thing I've heard about nanotubes.  Turns out the long thin types, if inhaled, might not be so good for our lungs.  Go figure.  I'm not sure why, but I can't picture this without picturing some hollywood movie star with rows of high-dollar carbon nanotubes and a rolled up $100 bill. 

Kidding aside, though, it looks as if nanotubes could possibly cause diseases normally associated with asbestos, like Mesothelioma.  Downer to the story is that it isn't as sexy as the one about the antimicrobial carbon nanotubes that break off and go rogue, killing cell after cell indiscriminately.