I have also had an bad and expensive experiance with FMF, I bought a Gnarly for my 2002 KDX, after only a few weeks my bike would not turn over.
I opened it up to find my piston and barrel was smashed, there were small metal fragments everywhere, so I split my crank and found pieces of welding splatter and a piece of Co2 welding wire. I suspected it was from my FMF pipe, as there is no welding in a bikes enjine. I shook my pipe and more welding splatter fell out!!!! On closer inspection I noticed that the welded seam along the top of the pipe was of bad quality. I e-mailed FMF and explained my story, they requested pictures, which I sent to them, and that was the last I have heard from them, that was in March 2003, I have tried to contact them at least ten times since, but I am obviously not importent enough to them, it might be the fact that Im from South Africa, and everyone thinks that we still live in the bush and hunt lions......but we have computers and KDX 200 in our caves!!!!!!