Regarding hardware vs. software...some of you may have seen my posts in this thread from the past, but in short, I had major issues after upgrading to Yosemite. I then insisted my motherboard be replaced and was met with NO resistance by the genius despite not being able to reproduce the problem. My replacement is about a month old and I have not had a single crash. Truth be told, I still had the transparency setting reduced, but I changed that a week ago. Still no crashes. I'm using it normally and NO CRASHES. How could there not be a hardware component to this problem under those facts? I've said it before and I'll say it again. This is how the software hardware scenario fits with the facts:
1) A small percentage of people are affected. Yes, we're all on this thread going crazy, but if it affected EVERY MBPr, it would be major news. If it were ONLY software, it would affect all those using MBPrs and Yosemite. This is not the case. This means only a small percentage of motherboards were built with the defect and because it affects new MBPrs, they are still making some defective boards.
2) Some people are "cured" with a hardware replacement. How do you explain this if it is ONLY software?
3) Some people are not fixed by new hardware. Why? Because they got a bad replacement as well. Clearly they are still making bad boards.
The bottom line is that there is a relatively small percentage of MBPr motherboards that are defective. Under Mavericks this defect does not manifest itself in a crash. Under Yosemite the defect manifests in a crash when switching from discrete to integrated and back. Apple is remaining silent on this because it only affects a small percentage of customers. Think about it, how many people does this thread represent? Virtually nothing compared to the hordes of people using MBPrs. Sure not all of them affected are complaining. They are lighter users who crash every now and then and just blame themselves. We know better but we're 100x more sophisticated than the typical user just by virtue of following this thread, and for 100 other reasons we could all probably recite.
Sooooo, the word is out to the "geniuses" that when a customer comes in with a video crash issue, replace the mobo without hassle, and hope for the best. Why don't they fix the issue in software? Must be more difficult than we would think...because there IS a hardware component to the problem. Why don't they fix the hardware? Too expensive to re-engineer the mobo I would imagine at the next major hardware revision, this will be addressed. For now, the dollars and sense analysis fell on the side of Apple remaining silent and just replacing motherboards for anyone who asks.