Can anyone tell me if the on~die thermal diode is accurate?. or does it all boil down to the chip reading it?

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I've noticed abit of banter about CPU temps here and am thinking why nobody uses the on~chip diode?. I know of only one mobo that supports it(and I can't remember the name!) , but the mod to make one is'nt that hard is it?.
Perhaps someone would start knocking them out? Hmm?...