It seems that this Science paper has received a whole lot of press...  I'd like to follow-up with some compelling multimedia from the various press releases. First, the photo below shows a "carbon nanotube aerogel artificial muscle" being pulled from a forest of carbon multi-walled nanotubes (MWNTs). 

Anyway, Wired Blog has posted a few choice videos (below), though I'm particularly fond of the commentary in the article by MIT Technology Review.  

Here are the videos:

And here are some choice quotes from the MIT Tech Review article:

The new actuators, on the other hand, expand by up to 200 percent but generate small forces per unit area, making them less than ideal for many applications, including robotics. However, their novel properties, especially their temperature range, could open up exciting new applications. "No other actuator technology can provide actuation at these extreme temperatures," Baughman says. "And these actuation rates are giant."

So the paper's primary author confirms my previous musings: this material may not have much utility as terrestrial robots' artificial muscles.  However, perhaps the other applications will be sufficiently compelling to spur additional research that may prove fruitful.

Qibing Pei, a materials-science and engineering professor at the University of California, Los Angeles, believes that the material could be a good candidate for shape-changing aircraft wings. Pei has developed polymer actuators that expand by up to 400 percent and work between -40 and 200 °C.

Since the nanotube ribbons are ultralight and can handle extreme temperatures, they could perhaps also be useful for making shape-shifting spacecraft parts, says Yoseph Bar-Cohen, a senior research scientist at NASA's Jet Propulsion Laboratory, in Pasadena, CA. "It's exciting that the material behaves this way over a wide temperature range," he says. "On one side we have Mars, and on the other side we have Venus. Their temperatures are within the performance range of this material."

The ribbons will probably still need to generate more force before they are practical for many applications. Right now, they generate 32 times as much force per unit area as heart muscles, which is a lot for their nanoscale dimensions, says Ian Hunter, a professor of mechanical engineering at MIT. However, electroactive polymers generate up to eight times as much force per unit area as the nanotube sheets. "For artificial muscle, you need a large change in force coupled with a large change in length," Hunter says.