A paper addressing this issue was published here.
"The goal of this paper is to answer
questions such as the following: How
common are memory errors in practice?
What are their statistical properties?
How are they affected by external
factors, such as temperature and
utilization, and by chip-specific
factors, such as chip density, memory
technology and DIMM age?"
And this is a part from summaries:
"This either indicates that chip size does not play a dominant role in influencing CEs or >there are other, stronger confounders in our data that we did not control for." >Similarly, "In all cases, for the same utilization levels the error rates for high versus >low temperature are very similar."
I would still recommend ECC for production systems, mind you.
