My husband loves to play the stock market. He picks what he considers to be up-and-coming companies that few people have heard of yet, or undervalued blue chips, and buys up their shares. As he puts it, he likes feeling like he has an "ownership stake" in companies.

Sometimes, his strategy pays off. His initial investment of $5,900 more than doubled between 2005 and 2007. He bought Apple at $65 a share and watched it climb to $190. The start-up 24/7 RealMedia doubled and he sold it before it plunged. His oil companies enjoyed record profits. But he often loses big, too.

Even before the October 2008 stock market crash, his investments had lost a third of their values from their peak. He erred in choosing the GPS-seller Garmin, which enjoyed great success until it lost ground to cell phones and other handheld devices. His investment in AIG, the insurance company that got a giant government bailout in September, fell to half of what he paid. First Solar, which develops solar technologies, went from $260 per share to below $100, but he still believes it's going to make a comeback.

I'm not so sure about that. But I also don't really care. And that is the beauty of our money system.

It's not that it's not my money, too—it is. But after realizing, as many couples do, that our financial habits aren't identical, we decided that creating a mix of separate and joint accounts would be the only way to let him invest in the stock market while I ignored it. Some couples need separate bathrooms or even beds; my husband and I needed separate investment accounts.

Here's how it works:  For the most part, all of our money is combined. We share checking accounts, credit cards, long-term investments, and savings. But when it comes to his stock market account, I don't get involved. It holds the same cash that it did when we first got married, but if we ever need it—in an emergency or to buy a house—then it will revert back into our common funds.

We didn't always have such a drama-free arrangement. Shortly after we got married, I argued that we should keep more of our money separate. I had a savings account that I started building up at age five; couldn't that remain under my name only? But at the same time, I wanted him to share all of his pre-marital savings. In her book Flux, Peggy Orenstein describes a similar urge, and points out how unfair it is: "Too often…particularly in the early years of our marriage, I viewed my earnings as mine and Steven's as ours. I wanted to be equal partners, but… I also wanted him to take care of me."

We should have had the big money talk—in a coffee shop. Financial experts say that just as you don't want to bring up sex suggestions in the midst of an intimate moment, you also don't want to talk about money habits when you're in the middle of a big transaction. Bringing up the subject on "neutral" territory like a coffee shop can help avoid flared tempers.