http://testallthings.com/2009/05/20/the-false-gospel-of-john-piper/
http://standingfortruth.wordpress.com/2010/04/01/john-piper-falls-deeper-into-the-pit/
http://www.thepathoftruth.com/falseteachers/john-piper.htm
Oh, boy, not the Arminian (God is not sovereign) vs. Calvinist (God is sovereign) controversy again.
The third site in your list says this :
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One of the biggest and worst lies ever told in manmade Christianity, one that John Piper subscribes to and teaches, is that there is a place of interminable torment and punishment for sinners. Men think to find this doctrine in the Bible, but while it is something the carnal man would wish on others, it is surely not something God has ever said or that ever entered into His mind. He made creation as an act of His love. He so loved the world that He gave His only begotten Son for it. We are His, bought and paid for by His blood.
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Looks like that site does not believe God allows people to go to hell... who is the heretic really?