New details were released for the upcoming Guitar Hero game coming this fall. The have confirmed that all four versions of the game (PS2, PS3, 360, Wii) will feature online play and downloadable tracks.
Aside from that, it was announced that a guitar attachment is being made for the Wii version of the game, though they are looking into other uses for the motion in the wii controller as well.
How they could possibly have both a guitar and motion incorporated, leads me to believe that there will be a cradle for the controller on the back of the guitar, and something like shacking that guitar would be detected by the controller. Or at least that's my theory, as of now.