First off - no luck needed on my XPS. I've had this laptop for 7-8 months now without any major problems. As far as DELL replacing the GPU, I didn't hear anything about it.
2nd - what is the failure rate of the 8600M ... and what is the failure rate of the 9600M? What is the real problem of the 9600M? Are you running such GPU? what problems are you experiencing?