This article claims that the WD MyBook Live uses Debian and is easily rootable:
http://www.smallnetbuilder.com/nas/nas-howto/31828-fun-with-rsync-and-more-on-the-wd-my-book-live
And the bottom of the manufacturer's support page seems to confirm that:
http://support.wdc.com/product/download.asp?groupid=902&sid=132&lang=en/
I don't have any first-hand experience with it.
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Eric Cooper e c c @ c m u . e d u