We've looked at what defines "rich," the affluent's attitudes about saving, and even what wealthy people buy when they go shopping.

But when it comes to day-to-day money decisions, it appears that the lifestyles of the rich and not-so-famous are, well, kind of blasé. They don't live in McMansions or drive Hummers to the gourmet grocery store. They work hard for each paycheck and make everyday decisions to keep their credit cards securely in their wallets. Want to track a millionaire in her natural habitat? Peek out the kitchen window and take a gander at who's next door.

If you haven't heard of the book The Millionaire Next Door, you're due for a trip to the library.

Fellow Fool writer Whitney Tilson consulted the book when he wrote about the habits of highly successful savers a few years ago. The characteristics of the average Joe Millionaire are worth repeating:

  • "More than 80% are ordinary people who have accumulated their wealth in one generation. They did it slowly, steadily, without signing a multimillion-dollar contract with the Yankees..."

  • Less than 20% inherited more than 10% of their wealth, and more than half never received a penny of inheritance.

  • They "wear inexpensive suits and drive American-made cars. Only a minority... drive the current-model-year automobile."

  • About half have lived in their current home for 20 years or more.

  • 80% are college grads, and 38% have advanced degrees.

  • 20% are retired. Of those still working, about two-thirds are self-employed -- mostly entrepreneurs, but also self-employed professionals, such as doctors and accountants.

  • On average, they invest nearly 20% of their household realized income each year.

  • Their median annual income was a mere $131,000.

Nothing too terribly eye-opening in that list, is there? What really sets millionaires apart is one simple mantra: Spend less money than you make.

Are you a millionaire in the making? If, like in the book, you answer "yes" to the following three questions, you may be well on your way:

1) Were your parents very frugal?
2) Are you frugal?
3) Is your spouse more frugal than you are?

If you're stumped for ways to cut back an already stretched budget, check in with the folks on the Living Below Your Means discussion board. (In true "Millionaire" fashion, you can try it out for free for one month.) They'll make a millionaire out of you in no time.