Presidential candidate and Governor of Texas, Rick Perry, recently told a group of voters in Iowa that Social Security is "a Ponzi scheme." This is an argument often made by those who wish to destroy Social Security, which is not an "entitlement" either. It's a form of retirement insurance that we've paid into, throughout our working lives.
Nic Baumann, at Mother Jones created a handy Venn diagram that shows the difference between Social Security and a Ponzi scheme:
cross-posted at MainSt/workingamerica.org