There have been many attempts at debunking the corrupted cone of learning, linked below are but a few examples. While each of the authors has done a nice job in their own way, my personal favorite is the image below, which summarizes things quite succinctly.
Retrieved 7/5/2014 from: http://temporal.pr0.pl/devblog/download/posts/bzdury/bullshit-cone-of-learning.png
What is also fascinating are the statements by folks who realize that the percentage cone can't be authentic, but use it anyway. Some examples:
"That being said, I’m sticking to my plan even if I may have been wrongly influenced by these percentages."
"So why is it – even though I now know that the percentages are a work of fiction that I really want it to be true – that I still believe it?"
"I will continue to use it [the percentage cone] until you can prove it is not true." (as opposed to I will use it only if I know it to be true)