When it all seems so basic and so reasonable, do you really need lawyers? Well, yes, because if you do it yourself—and the internet is happy to help—you risk painting yourself into some weird legal corner where you're worse off than if you'd had no agreement at all.

Things vary from state to state (some, but not all, have adopted the Uniform Pre-Marital Agreement Act). Like Spielberg's napkin, homemade prenups may not stand up in court anyway, so if you're going to do it, you might as well do it right.

In fact, experts urge that each party have his or her own lawyer. "Interview three or four," advises Nachshin. "Get somebody who your [future] spouse's lawyer can work with; you want to avoid antagonism." Ask them, he insists, how many prenups they've handled. "The lawyer who drafted Barry Bonds' first agreement had never drafted one before," he says, with the hindsight of a man who later had to defend it in court.

And, speaking of protocol, do you need to tell your friends or family about your prenup? Only if you want to complicate things. "Once you bring it into the family structure, you'll get five opinions," says Altman, "which can create static and misinformation."

Honesty is key. Each person needs to spell out exactly what they're bringing into the relationship, both good and bad. If there hasn't been full disclosure by one of the parties, the court may throw the entire agreement out. Everything gets laid on the table—debts, inheritances, and assets—so there are no surprises. And the process reveals which values are ultimately the most important, like compassion, caring, and fairness.

A happily prenupped and married woman named Melissa describes a best-case scenario: She and her husband talked about their prenup even before they announced their engagement. "That was ten years ago," she says. "At the time, a friend of mine said, 'That's the most loveless thing. It's so cold.'

But we were grown-ups who had some of our own stuff outside the marriage as well as our own careers, and we really married for love. We didn't have any craziness, and we essentially agreed that what's yours is yours, what's mine is mine. I always say that, God willing, we'll never have to refer to it—and we never have."

Prenups should be thought of as living documents, though. Women end up raising kids instead of developing a career, the struggling author becomes a best-selling screenwriter, a business grows or busts. Some things won't become clear until later in the union.

Attorneys advise couples to revisit the agreement and update it as necessary. "As people change, the prenup should change," says Altman. At some point, she adds, after you've been happily married for 25 years, you can tear it up.

Call me a hopeless romantic, but that sounds like a worthwhile goal.

*Names have been changed.