Reply #19: So what happens to the money you put in if you die before retirement age?

[Major Nikon]

Also there isn't a linear arrangement between what you pay vs what your benefit is. The more you pay over your lifetime, the less benefit you receive dollar for dollar. This is because of the bend points the SSA uses in the PIA formula.
http://www.ssa.gov/oact/cola/bendpoints.html

SS is really more of a taxpayer funded insurance plan, which means the premiums you pay are a tax.