What exactly are you listening for?
Is it when they go so far out you hear a wobble like in that famous Cher song?
Anybody link me to one of the X-factor performers who it was very noticeable on because I've still got it recorded.
There was definitely a processed vocal wobble on the last woman performer but I can't remember hearing it on anybody else (there again I did come in from my gig a little bit drunk).
The first "good" performer - black girl with sob story had pitch corrector, you can hear her "straights" - the long notes - immediately hitting right on the note and remain perfectly, precisely on the note for prolonged periods of time, which, as you know from practice is actually not possible to do in regular registers - human voice, similar to all string instruments (including keyboard instruments using strings) is based on vibrations so by default notes are off pitch by tiny amount. You have to go very high vibrations - violine high - for human ear to start loosing that sinusoidal "air" and "breathing" of the sound and hear it as constant "still" note, and even then players vibrate notes slightly specifically so they go in and out of pitch and don't sound "odd". Only electronic instruments hit notes right on the nose, which is why pitch correctors always sound synthetic, like old, pre sampler electronic instruments.
Then you had the awful bad crazy man with fat girl doing the Journey song reinvented as duet by "Glee" Tv series - girl was put through autotune. This might have been done in post production, to make the difference between the two more pronounced, but it had crazy bad setting. Auto tune doesn't have to sound bad, many producers use it for "dynamic" effect - kind of like with young artists - Demi Lavato or Selena Gomez, you correct delivery and end target for louder notes, which would be out of range when sung with force by otherwise fairly competent, if a little inexperienced artist. You cover the effect up with overdub, preset to create harmony - bang - it's not that obvious to notice, and the song can then be done live without any issue, it just means you'll need to get back singers to carry the part while the "star" will sing lower. Trouble starts if you do it with little care and detail - no progression, just hit that note, than proceed to second note. This is not a keyboard, you don't go from A to G in a sudden switch, voice does not goes from one note to another in a square jump - it will sound like Cher, which is now 12 year old production and, funnily enough, back then was actually done by an error in Antares settings.
And then finally the crazy "mercy" girl - I think it might have been done live, because autotune was just crazy evident, going bonkers with sudden, square sounding pitch elevations and "pitch search gurgling" - something that made
Lil Wayne famous - since you have to set the corrector against something, some tune - if it's done manually live or without predefined harmony - it will go bonkers since it means both person corrected and person correcting are desperately searching for common tune.