Another thing you might want to check is how well ventilated your Pi is, high temperatures might also toast cards.
I did have trouble running a USB drive that worked everywhere else off them, so perhaps power is the problem and that not working was due to it being more hungry and other drives and the Pis not having enough amps spare to hand over.
This wasn't filesystem corruption though: the SD cards never worked properly again so there was presumably some physical issue rather than just damaged data. I can't say I've noticed any part of them being at all warm either in general running or after a card had died so if it is heat related the heat was temporary (and they aren't where things like direct sunlight or near-by household heating could be a variable).
I'll check the power supply at some point, but for now they've both been running smoothly 24/7 for months so I'm happy with the NFS solution for the time being.
As far as I know there's a task running on the "GPU" (where quite a few things are assisting the ARM CPU showing the screen, playing audio, actually bootstrapping the ARM, ...) that provides this icon as a feedback to the user.