[id10t]

I've had "not bad but not good enough or quite the right spec" ram a few times, but usually only in multiprocessor machines, and never when using the specific ram the manufacturer of the motherboard recommends (usually crucial). Only thing I can think that may be causing it I've seen happen on XP laptops, where the suspend/sleep area is actually a separate partition that must be the size of the memory, since it dumps all ram contents to disk when it sleeps. Add ram, and you suddenly have problems if it can't read back in something from ram it needed as opposed to missing something that wasn't in use, just cached from the last use. Note that I'm not sure how OS X does "sleeping" or how it manages memory that isn't being actively used (flush, cache, etc).