I am in the process of getting an RMA for my Phenom II x4 965 BE as the memory controller will not let it run in dual channel. In emailing back and forth with AMD I was asked what cooler I use with the chip. I told them that I use an Arctic Cooling Freezer 64 Pro, to which I was told, "Please be aware that using a third party heatsink does void the warranty on your processor. However my manager has agreed to allow a one time courtesy replacement since your issue is not tied to a cooling issue.
This was the first I had EVER heard of this, so I looked it up this morning:
"This Limited Warranty shall be null and void if the AMD microprocessor which is the subject of this Limited Warranty is used with any heatsink/fan other than the one provided herewith.
So, it seems that, in order to not violate the warranty, you have to use the jet engine cooler that comes with the chip. Or at least tell them that you do.