Does this really matter in 2013? Serious question. I could see ECC having been useful in 2000 in the midst of the megahertz race, but I'm not too convinced about today...
The probability of a bit error on normal RAM is quite high [1]. The more RAM you add the more likely you are to see corruption. Not that ECC fixes everything - I still see uncorrected ECC errors on the older HPC nodes on our grid.