Bush's regime has been claiming that, under their plan, someone who invested their privatized Social Security and got a 3% return would break even. If you did better than 3%, you'd be richer at retirement, they claim.
But that is a meaningless statement, since, at present, Social Security is mildly redistributive - the poor, and the married, do better out of it than the single and rich. Take a look at the table from "Ask an Actuary" - government figures, back from December 1994 (when government employees could tell the truth without getting sacked):
http://www.ssa.gov/OACT/ASKACT/part2.html(note that the table assumes various growth rates, like 6% interest, that apply to everyone, so the important comparison is the relative gain/loss by the different categories of people, not a single person's taxes and benefits).
A low income married man with a family does the best - he roughly doubles his money; increasing income, or being single, means you get less, compared with your input (a single man on the maximum income loses roughly half of his money, assuming the 6% growth).
So, if you switch to a system in which the benefits are directly proportional to the amount of money taken in taxes from you, those earning the maximum amount for the Social Security tax will do better, while the poorest workers will have to get a much larger rate of return if they are to get the benefits they do now.
Bush's attempt to privatize Social Security will hurt the worst off in society the most. No surprise there, but the main argument has been "would the money grow faster in the stock market?" The fact that Bush wants to make the rich-poor gap even larger than now is going unreported.