I found this link, from April 2010:
Reinventing the Wheel: a Guide to Michelin’s Airless Tire - autoevolution
Please do have a look, this is a fairly informative article. It includes this:
"...One of its biggest flaws is vibration. Above 50 mph, the Tweel vibrates considerably, thus generating noise and heat. A fast moving Tweel is reportedly unpleasantly loud. Long distance driving at high speeds generates more heat than Michelin engineers would like. That’s why, for the moment, the first applications of the Tweel are in low-speed vehicles, such as construction vehicles. ..."
I thought I saw an announcement that the tire was to be released this fall (2011). But a google search turned up nothing on that.