When we went to Disney, we saw this in the gift shop, and the kids thought this was cool. The price was not bad considering other things in their gift shop.
This string thing toy has a built in black light that glows in the dark. When illumimated it curls, crawls and does tricks with one motion of your hand. The unit comes in 5 different colors and has a display base for the table top. We use it outside at night because the neon colors or so colorful. Battery operated with 4 AA batteries-average battery life time for these kind of units. An independent power/light control, with built-in AC adapter jack(sold separate), and 3 LED Black Lights and reflector(which illuminates the moving string.
While this was a cool purchase, we have found that it tangles easy, and that takes some of the enjoyment out of playing with it. We used it on 4th Of July with all the other colorful sparklies and the Breast Cancer Walk (All Night), and got comments on how much fun and colorful it was, so I'll rate it with a 8 out of 10.
Update On Jul 02, 2010: Here it is almost the 4th of July and time to play with this before the fireworks start. Kids that sit next to us always like to see how this makes different shapes and the colors are quite colorful.