Guitar Hero III is already a huge success, having sold over $100 million of product on Wii, PS3, Xbox 360, and PS2 during its first week of release. Sales probably won't be too shabby when it releases on PC and Mac next week, either.
According to Jesse Divnich, analyst for The simExchange, the Nintendo Wii version is predicted to outsell the PlayStation 3 version by a two-to-one margin when all is said and done.