U.S. News & World Report: Individual retirement accounts held an estimated $4.7 trillion in 2010, which is just over a quarter of all retirement assets in the United States. Some 49 million Americans had at least part of their nest egg stashed in an IRA last year. How well you choose IRA investments and minimize taxes using these accounts will play a big role in how prepared you are for retirement. Here are 10 things you should know about your IRA.