Also bundled with the pre-order offer is a GameStop-exclusive in-game guitar, which possesses a "unique, sexy body inspired by the members of Tenacious D." We hope this means Jack and Kyle gave their input on what the guitar should look like, and not that the guitar actually looks like their bodies. We're doing just fine without that mental image, thanks.
Update: While the demo access is new information, we actually knew about the gee-tar in May. We've even got a picture of it -- and we're happy to report it doesn't feature nude versions of K.G. and Jack. No, wait! There they are!