There are over 36 million different birthdates registered with the site. And, if everyone is telling the truth, one out of every 12 Ashley Madison members was born on New Year's Day.
January 1st is by far the most popular day that members said they were born, presumably because the site asked visitors to pick month, day and year and people only bothered to change the year. Those who did change the month and day, though, often picked the same number for each: February 2, March 3, April 4. After all, it's as easy as hitting 6-tab-6 on most computers.
Oh, but some of the truly romantic people looking to cheat on their wives got a little more creative: 124,000 said they were born on Valentine's Day. (Update: And, as someone on Twitter pointed out, on April 20. Ahem.)
More evidence that people simply made dates up? Every day in January and the first of every month were disproportionately popular as people who were not quite lazy enough to leave the birthday selector at January 1 changed either the month or day.
Other patterns hold in both the dates and the years that people offered up. Multiples of five were common -- 1965, May 20. The most common year that people gave was 1978, by a wide margin. More people said they were born in 1978 than said they were born on January 1. The most common decade for people to say they were born was the 1980s, the children of the "Me Generation." Or, at least, older people that want people to think they're that young.
We'll add an important caveat. We can't necessarily extrapolate from this data to web users on the whole. After all, the entire site is predicated on deceit.