Through liberal use of Demonic Empowerment (and its associated threat bug) and their awesome healers, Mister Voidwalker successfully tanked the Priestess mob in the Illidari Council encounter and most of Illidan himself. An incident with Parasites caused a little chaos, which ultimately spelled the voidwalker's demise. Illidan hits juuust a little too hard to live through a few of the healers scrambling away from parasites. Even if it had 23,000 HP.
It was also mentioned in the e-mail to us here at WoW Insider that they used the Voidwalker to tank the first three bosses in Mount Hyjal as well. I think even a baby kitten could tank the first three bosses of Mount Hyjal nowadays, but using a Voidy for it is still pretty dang cool. I hope to see more off the wall stuff like this before Wrath launches, so if you have it, please send it in to us!