No the screensaver is not the problem, but it is probably the best way to replicate the issue. It can take minutes or days but it will crash eventually if you leave Flurry running.
This. Further, it seems to be something the Apple techs are able to set up and recognize. I am totally confident that the machine would freeze just sitting there doing nothing, but when that was the plan, for whatever reason, Apple was never able or willing to get results. Having them do the screensaver was the crack that broke the dam.