Well, I recon it might've been used on Bono in the U2 and MJ Blige One duo.
I noticed in the Rose Bowl dvd there was a very slight use of it in a couple verses of one or two songs.
I can't say for sure, but I have a pretty discerning ear and I can really tell when autotune (or melodyne - a newer, more controllable form of autotune) is used. I never noticed it in any of the songs on NLOTH, Bono sounding slightly
strange may be due to the some of the songs being really distorted from being so loud (basically like pushing an amp and speakers too far and they distort... now imagine that on a cd and thats what most music today is like, well, its not overly noticable but in some songs its painful for my ears)
Personally it really isnt necessary, perfect music is never that great... its the slight inconsistencies that make it real...