Million dollar incomes on the rise again

The number of millionaires in the U.S. is moving on up.

There were nearly 268,000 tax filers who reported more than $1 million in adjusted gross income in 2010, according to a Tax Foundation analysis of Internal Revenue Service data.

That's about 31,000 more than the previous year, but is still lower than the boom times. Between 2005 and 2008, the number of millionaires topped 300,000 annually.

The vast majority of millionaire taxpayers are married and older than 45.

Millionaires had just 10% of the total adjusted gross income in the U.S. in 2010, and they paid 22% of the taxes.

But most of these millionaires don't stay in this elite club for long. Only 6% kept bringing in the big bucks each year between 1999 and 2007, while 50% did so for only one year. They can thank the ups-and-downs of the stock market and the strength of their businesses for that.

"Taxpayers move in and out of millionaire status with great frequency," the Tax Foundation wrote. "The volatile nature of capital gains and business income appears to be the leading factors for the transiency of millionaires."