The origin of this quote seems to be an article by Hildi T. Kelsey, August 31, 2006, in a News Bulletin of the Los Alamos NAtional LAb. Lets look at some numbers (from http://en.wikipedia.org/wiki/Tensile_strength)
Material Yield strength (MPa) Ultimate strength (MPa) Density (g/cm³)
Structural steel 250 400 7.8
Carbon nanotube N/A 62000 1.34

So on those numbers nanotubes are 150 times stronger for 1/6th the weight.
The LANL progress (led by Y T Zhu) is spinning the fibres into tubes up to 4 cm in length. Just as a rope is less strong than its individual fibres, so I guess spun tubes from nano fubres are less strong than the fibres, hence the 100x figure and its weight is probably 1/4 that of steel. Hence, it looks like the author above slipped by one order of magnitude which is not too bad for a journalist in my experience.