These are actually quite good. I've dismantled one of these and fed the output to my car stereo ( along with the usual mp3 input) to cancel out the low frequency hum of the muffler and engine.
I've had better luck with this than another generic brand.
Note that noise cancellation works best for lower frequencies and may not work at all with higher frequency sources like car horn.

I've a skull candy headset on sale. if any one interested

search Skullcandy Com Ti Multimedia Headset on ebay. The auction starts at $55