Prenuptial agreements are not exclusively for celebrities, especially considering how they are used and the "interesting" clauses that have trickled down to everyday couples. For instance, so-called "lifestyle clauses" which can regulate how often a spouse's in-laws may visit, which spouse is responsible for certain chores, or even weight-limit clauses are being used in prenuptial agreements.
Perhaps the most popular lifestyle clause has to do with infidelity. Essentially, parties intending to marry may decide to include certain financial penalties if a spouse cheats. As a rumored part of her prenup with Justin Timberlake, Jessica Biel will supposedly pocket $500,000 each time Justin strays during their marriage. Also, Catherine Zeta-Jones is suspected to have a similar clause in her agreement with Michael Douglas.
According to a Forbes magazine report, more couples are using infidelity clauses in prenups because fewer courts are viewing infidelity as a reason to find fault in a marriage as a reason to grant a divorce. A majority of divorces are granted because the parties have "irreconcilable differences" and fault is no longer necessary to be proven as a ground for divorce.
Further, some couples may feel more comfortable establishing their own rules for their relationship, and putting a monetary penalty on infidelity is arguably one of the best ways to achieve this.
So an interesting question would be: could a prenup with an infidelity clause be enforceable? The answer depends on several things, including but not limited to whether each party properly disclosed all of their disclosure of assets, whether the agreement is "unconscionable", whether the signature on the document was obtained without duress and whether both parties had a reasonable opportunity to consult with a lawyer of their choice.