Basically, we have a "crisis" in social security only if you make very pessimistic assumptions about future economic growth (you assume growth will be only half of what it has been in the past). On such assumptions, at some point you won't be getting enough from the payroll tax to fund the system, so you will have to start drawing down the "trust fund" (in 2018), and at some point the trust fund will go to zero (in 2042). Thus, in the distant future social security funding will have to come from general tax revenues (which is the way the government funds everything else, of course, including Bush's salary and retirement benefits, and no one thinks that is causing a crisis).
Using the same pessimistic assumptions about future economic growth, the stock market won't go up much in the future, so "privitizing" by putting money in the stock market won't give much of a return. If you use the growth assumptions necessary to make "privitization" attractive, you also will have enough trust fund revenue in the future to keep SS in good shape. Interestingly, 10 years ago the government was saying the crisis would come in 35 years -- now, the government is saying the crisis will come in 38 years. At that rate, it never will arrive, even with pessimistic growth assumptions.
