I have tanked Razuvious once before, and it was successful. Moderately. We won the fight, but it was not elegant.
Three days after we did S3D, we're in Naxx and I'm up. We have no shadow priests and only two healpriests. I'm not terribly confident, and tell the raid leader that, but we'll go anyway. We're having a blast plowing thru the place. My tanking fails miserably, and we wipe. No big deal, but the raid leader is already offering to bring his priest.
Second try, this time with me healing and our raid leader priest-tanking, and it's a perfect kill. His spec was irrelevant, his skills apparent. No hard feelings, no big deal. After Razuv he goes back to his mage and we continue pwning.
(And if you were thinking "Ha! Vindicated!" or some such thing, then you missed the point of the previous post. Knowing when you're not the best man for the job is just as important as knowing when you are. Go team!)