(Business 2.0) – The Economic Growth and Tax Relief Reconciliation Act of 2001 contained many provisions that only a bean counter could love. But here's one you might grow fond of: the provision that lets you—while still employed—roll some or all of your 401(k) into an IRA through which you can invest the money any way you please.

As baby boomers' retirement savings swell, so-called self-directed accounts are gaining in popularity. Instead of picking from mutual funds in your company's plan, you can invest in, say, a fast-food franchise, an apartment complex, even an oil well. And any money you make grows tax-free.

So what's the catch? Besides the obvious—your retirement savings could vanish thanks to a dry well or a poorly located Chuck E. Cheese's—there are a few things to keep in mind. Unlike a regular IRA, which you can establish for free at many brokerages, a self-directed IRA must be set up through a limited number of banks or independent trust companies. As a result, management fees can be as much as 1 percent of your account's value. Also, anything you acquire must be used for investment purposes. Though you can buy a house with the money, for instance, neither you nor your family members may live in it until you hit retirement age.

As for how to put your cash to work, pros advise leveraging your expertise. "I get real estate developers buying and flipping properties, and doctors entering into private partnerships in imaging centers," says Paul Maxwell, chief operating officer of Trust Administration Services in Carlsbad, Calif. "People tend to invest in what they know." And if your money goes poof, at least you'll know where to find the idiot who's to blame. — MICHAEL V. COPELAND