I'm not sure how light the trainer is, but the 1upusa trainer folds up very nicely. On their website, they show a picture of it folded up -- it's only 6 inches thick because of the flywheel.

I use mine almost every morning these days. It's probably the easiest trainer I've ever used as far as set up and take down go.
http://www.1upusa.com/bike_trainer.html
-- Melissa
PS According to their website, the trainer is 16 pounds. I'm 5'1" and will never be able to beat Charles Atlas in an arm wrestling contest, but I haven't found this trainer cumbersome at all.
Last edited by melissam; 02-28-2008 at 10:35 AM.
I'll get back on the bike soon, I promise!