I was at Best Buy today and surprisingly they had a GH:WT guitar hooked up to a 360. No GH:WT game though.
The guitar was extremely solid and felt heavier than the Wii GHIII guitar I have. It seemed a little bigger as well, but I didn't measure it against anything else. The quality was top notch and the finish was flawless. The buttons are the same. The strummer felt a little more solid and wider. I was really impressed at the build quality and if the drums are this good, there will be no reason to buy RB instruments unless you want to play RB on the Wii.