Gametrailers.com [1] found that Metallica confirmed an exclusive version of Guitar Hero to be released in fiscal 2009.

All I know is, you better not download it, lest you face the wrath of Lars like the Napster people!

This is great news for anyone that wasn't satisfied with everyone at your Guitar Hero party endlessly choosing every Metallica song anyways!

Here is the original details from Gametrailers if you care:

Hetfield and Co. confirmed for exclusive

According to a recent SEC filing obtained by GameSpot [2],
Activision said it plans "to publish Guitar Hero: On Tour for the NDS;
Guitar Hero: Aerosmith, Guitar Hero: Metallica, and Guitar Hero IV
across multiple platforms" in fiscal 2009, which ends March 31, 2009.

With Guitar Hero: On Tour (Jun 22), Guitar Hero: Areosmith (Jun 29),
and Guitar Hero: World Tour (Oct. 27) already announced, the statement
marks confirmation of an official Metallica version of the popular
rhythm game, likely expected after the holidays in early 2009.