Caving to overwhelming pressure, Cindy McCain today followed the 2004 example of Theresa Heinz Kerry and finally released a two page summary of her 2006 tax return. A quick glance at the filing explains her hesitation to let her tax returns see the light of day. As it turns out, Mrs. McCain gave only 1% of her $6 million income to charity in 2006. Worse still, most of that went to private schools attended by her children.
Just two weeks after insisting she would "never" release her returns, Cindy McCain today reversed course and published a summary of her '06 return. (She has yet to file her 2007 return, having received an IRS extension.) As the Washington Post noted, the beer heiress estimated to be worth over $100 million generated $6 million more in income in 2006:

The returns show that she received a salary of $299,418 in 2006 and interest of about $40,000. She also reported taxable gains of $743,476. But most of her income -- $4,551,901 -- came from a category that includes rental real estate, royalties, partnerships, corporations or trusts. The campaign did not release documents that detail what that money is from.
The two pages of documents are the summary sheets from the 1040 tax form she filled out. It shows that she paid $1,746,445 in federal taxes in 2006.

But while the coverage today did not detail Cindy McCain's contributions to charity, the McCain campaign web site did provide some information:

"In 2006, Senator and Mrs. McCain donated $129,390 from community assets to charity, of which Senator McCain's one-half allocation was $64,695. This is 19% of his adjusted gross income."

Which means Cindy McCain gave only about 1% ($64,695 of $6,066,431 in adjusted gross income) to charity in 2006. That figure is less than half the 2.2% of their incomes Americans on average give to charity.
More damning is where the money goes. As Harper's reported in February:

Between 2001 and 2006, McCain contributed roughly $950,000 to the foundation. That accounted for all of its listed income other than for $100 that came from an anonymous donor. During that same period, the McCain foundation made contributions of roughly $1.6 million. More than $500,000 went to his kids' private schools, most of which was donated when his children were attending those institutions. So McCain apparently received major tax deductions for supporting elite schools attended by his children.

Documents released by the campaign show where the John and Cindy McCain Family Foundation distributed its money in 2006. Of the $187,639 in contributions made by the Foundation that year, $50,500 went to the Brophy College Preparatory School, previously attended by their sons Jim and Jack. Another $42,639 went to Christ Lutheran School, where Bridget and Jim once went.
In contrast to the 2% combined charitable giving of the McCains, Barack and Michelle Obama donated 5.7% of their 2007 income to charity. As the New York Times noted, the Clintons have not always met the 5% goal Bill Clinton set for himself.
Two weeks ago, Cindy McCain claimed she would never release her tax returns, even as First Lady. As she told ABC News, "This is a privacy issue." Today, we have better idea as to why.
Update: Several readers have noted that it is not possible to gauge the full scope of Mrs. McCain's charitable contributions based solely on the limited disclosure Friday. Her itemized deductions totaled almost $570,000, of which her giving to charity would be part. Bu without access to her Schedule A form (which she did not release) detailing those contributions, it is not possible to know what she claimed. So, Cindy McCain may well have given more than 1% of her $6 million income to charity in 2006 from separate assets. But without either the release of her full return - or a statement from the McCain campaign - we'll never know.