How reliable is computer memory these days?

olddoc writes: I remember reading about cosmic rays causing memory errors and how errors become more frequent with more RAM. That was in the days of 512MB systems. Now home PCs are stuffed with 6GB or 8GB and no one uses ECC memory in home PCs. Recently I had consistant BSODs with Vista64 on a PC with 4GB and I tried memtest86 and it always failed within hours. Yet when I ran 64bit Ubuntu at 100% load and using all memory it ran fine for days. I have 2 questions: 1) Do people trust a Memtest86 error to mean a bad memory module or motherboard or CPU? 2) When I check my email on my desktop 16GB PC next year, should I be running ECC memory?