In the email announcement I received about the release of Liftport’s February, 2006 Technical Newsletter, there was also an announcement about a study which had been done by Nicola M. Pugno (available here) stating that, because of “inherent defects” in a Carbon Nanotube cable, it’s maximum strenght would be no more than approx. 35 GPa. If true, it’s a problem. But only if it’s true. Liftport has started a discussion forum on this subject here.