This is just yet another PR attempt by GW Bush to scrap traditional Social Security and replace it with a more expensive privatized system run by his friends. In reality Social Security is in good shape, and every past projection by the trustees has turned out to have been overly pessimistic, even the best-case projections.
Some people claim that privatizing Social Security will help the economy in the long run by increasing the nation's pool of capital, but that's unlikely, and what really matters is the ratio of working people to retired people. The US is actually in better shape than most developed nations in this regard, mostly thanks to immigrants, and illegal immigrants may help even more because so many of them contribute to SS and Medicare but never collect.