AMD says no thermal grease
 

Apparently using Artic Silver, or any similar thermal paste on your AMD is now terms for warranty voiding. The ONLY thermal compound that AMD approves is Shin Etsu G 749. The reason is that most thermal compounds are made up of conductive particles which, if improperly used, can cause shorts on the processor. This is quite odd considering that AMD has tried to cater to the overclocking markets in the past.

Read more here

all you have to do is not improperly use it it.

Easier said than done. I saw a guy putting together a computer for a customer at the shop he works at, globbed on enough for 3 cpu's. This guy has put together atleast 25 systems, if not 50 or more - I can't believe how some people think if a little works good, a lot should work a lot more.

Personally I wish they would place a nice flat metal covering over the die and cover the rest of the chip so that heat would disappate (pardon the spelling, I know it's wrong..) over a wider surface - but given that they haven't done it I would assume there's some engineering reasoning why they don't.

-WC-

It's not true, I've returned a chip after using Arctic Silver, even told the guy on the phone I had used it, he wasn't happy, but didn't say anything against it. Found out that the processor wasn't even bad it was my mobo being screwy but AMD was cool enough to replace my processor anyway. AMD is good about their warranty and the above is either a new policy or pure FUD. Hell the proc. I sent back even had traces of Arctic silver on it, that stuff is hard to clean off. Been their, done that, running the replacement proc now.