For the first time since 1983, Social Security will pay out more than it takes in this year (2010). Decreased tax revenue caused by the recession is to blame. This situation should be temporary assuming that unemployment trends downward. A new tax on health care benefits will also help. The Congressional Budget Office currently estimates a date of 2037 for the end of solvency.
The huge demographic bubble of baby boomer retirees will take a toll on Social Security. There are 3.2 workers for each recipient today. According to the Social Security Administration, that number will drop to 2.1 by 2034.
The fund for Social Security has a surplus which will take care of negative balances (including this year), but the money will begin to completely dry up when the program's solvency ends.