Facebook plans to announce it has reached a milestone 500 million users this week — but that doesn’t mean the masses are happy customers.

The American Customer Satisfaction Index, developed by the University of Michigan’s Business School, included Facebook in its regular survey of consumer satisfaction with companies.

The result: Facebook came out with one of the lowest ranks of any company measured by the Index – a 64 out of 100. That puts Facebook in the bottom 5% of all private sector companies, and in the same range as the IRS tax e-filing system, airlines and cable companies.