It's likely the wave of the future. As exotic woods become more scarce, alternatives like this will replace them and hopefully get cheaper.

Here's one made out of Granite

http://www.squidoo.com/graniteguitarurn

Okay, so it's a cremation urn. But with a nice set of strings...

I was looking for an actual Granite Guitar I'd read about built by some university, I think. It was supposed to have had ultimate sustain.

But I think I am getting off topic. It's too bad there are no sound clips with the ad. There are actually some reviews at Harmony Central on Rainsongs. here is the only one on that model...
http://reviews.harmony-central.com/reviews/Acoustic+Guitar/product/Rainsong/A-WS1000/10/1