From Time.com: "Superstitious Americans…have gone to great lengths to secure the triple sevens as their wedding date, hoping the lucky numbers will make them lucky in love…It may well be the most popular wedding day in history."
Since the demand for weddings on this date was high, the price for 7/7/07 weddings should also have been high compared to other dates. Thus, only couples willing to pay a superstitious premium got married on 7/7/07. This could provide a great research opportunity. Are superstitious couples, for example, more likely to get divorced? Do they make as intelligent financial decisions as other couples do?