C. Doug,
Didn't Greenspan himself expand on the terrific rate of return retirees have gotten from social security up to now? I'm sure I heard something like that in his recent testimony. He also made the interesting point that it really didn't matter that the government pension plan (social security) only invested in government bonds since the overall mix of securities in all pension plans (private and public) would remain relatively unchanged. So long as there is a fairly stable amount of stock available and absent a very large bubble, he's right it seems to me.
Of course that means the poor people are "investing" in the lowest-yielding, most secure instruments, (through social security) but they're on a defined benefit plan anyway.
peace