I have to concur with
@Wolfshadw - while I have gotten a used system that already had a bad RAM stick, I don't think I've ever personally had any RAM go bad.
And, similar to Wolf, I've got an old Slot 1 based system with a Socket 370 adapter, has had various Pentium III and Celeron CPUs from around 600MHz to the current 1GHz Celeron. Running a mismatched set of 100MHz SDR RAM (all the modules are 100MHz CL2, though, but, in the 3 slots, there are a 256MB, 128MB, and 32MB stick, respectively, for a total of 416MB of RAM).
Still runs.
I haven't fired up my old AMD K6-2+ 400MHz system, that's got a 128MB and a 64MB stick of 100MHz RAM, and was working when last fired up about 8 years ago.