From the extensive New York Times account of Mrs McCain's finances --
How much she receives in profits is not a matter of public record. Distributions to other shareholders, who discussed them only anonymously, suggest she receives hundreds of thousands of dollars several times a year. Mrs. McCain has released only a two-page Form 1040 from her 2006 return. It listed $4.5 million in income from S corporations (like Hensley), partnerships, rental real estate and other categories; capital gains of $743,000, and dividends of $283,000.
A S Corporation is a corporate entity that passes through profits to its shareholders without any corporate income taxation. Thus it avoids the so-called double taxation of corporate income at both the company and owner level.
A S corporation is also George Bush's favourite rationale for his tax cuts for the rich --
What I don't think a lot of people in Washington fully understand is that small business owners are going to bear a heavy burden if the tax rates go back up. And the reason why is, is that most small businesses owners are Subchapter-S corporations, or partnerships, or LLCs, that pay their business taxes at individual rates. So if the individual rates go up, it directly affects millions of small businesses in America.
There are many problems with this logic, not least how poorly targeted his tax cuts are at actual small businesses. But Cindy McCain makes a nice counterexample, paying lower taxes on money she gets as a passive owner of an inherited business (a transfer that survived the USA's Communist estate taxes) and then spends on accumulating so many houses her husband can't remember how many there are.