Some games just don't lend themselves well to eyefinity. Diablo 3 has fog of war on undiscovered territory and the extra viewable area wouldn't even be helpful since you're focusing on your character. I think people are just looking for stuff to complain about.
Plasma has great blacks but what fans will never tell you is that all plasmas dim the screen aggressively based on white (or near white) content. You start to see the effects at like 10% white pixels.
Are there certain brands that are better than others in this regard or is pretty much a crapshoot (I'm guessing the latter)? Or is electrical noise pretty much inherent to a power supply? I guess this is more of a brand question than particular units.
edit: Sorry meant noise that you hear.
I've seen temporary image retention on my Nexus S, but never any burn-in. I wouldn't worry about it at all. The Lumia 900 has a non-pentile amoled so it should be great.