Joshua Claybourn's Domain links to an article showing that mixed-faith marriages have substantially higher failure rate. The article states:

The American Religious Identification Survey 2001 (ARIS) finds that of all U.S. adults who have had children with someone of another faith, 10% are divorced, compared with 3% for parents of the same faith.

Those numbers seem awfully low compared to the 50% divorce failure rate in society generally.

Josh's take is "duh?" But I don't know. I don't think I ever dated a Catholic. I married a Protestant gal, and I was never more surprised than when our priest made us sign the contract that the children would be raised Catholic. I had thought that that was another urban legend. On the other hand, that was really the best thing that anyone could ever have done.