you can also run the apple hardware test. http://support.apple.com/kb/ht1509
it may actually show a problem with the RAM.
i would at least set up a support request to get the Apple RAM replaced (if it was Apple RAM) and document the issue.
if it randomly starts to kernel panic (i assume that's what you're calling "grey screen of death"), you can take it to an apple store to request diagnostics be run. the service diagnostic is very thorough and can catch weird problems.
hopefully it was just the RAM. :)