Here's the wiki page, there was a thread on the escapist not long ago about bitcoins, if you use the search button you can find them and read through what everyone said. http://en.wikipedia.org/wiki/Bitcoin
Judging by the way the currency is generated it doesn't look sustainable at all, just read the critisms section of the wiki page. They also claim that the number of bitcoins will be limited to 21 million. It will probably be quite lucrative until the system hits a crisis point, and then in an instant the whole thing will crumble, leaving the investors and users with quite a large hole in their wallets.