Metal Injection reports that Slash of Velvet Revolver and Guns N Roses fame will be a playable character in Guitar Hero 3. To play as Slash, who did motion capture for the game, you have to complete all of the songs in the game and then face him in a one-on-one duel. No idea what sort of cred Metal Injection has and they don't list a source, but it sounds very conceivable.
Slash to Appear as a Character in Guitar Hero 3 Video Game [Metal Injection, via GayGamer]

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