Recommended: OKCupid’s OKTrends Blog

Most people know OKCupid as a dating (and general social) site — but they also have a wonderful blog called OKTrends. Because the site is so large they have an enormous dataset. Because they are interesting people, they regularly slice and dice this data set in interesting ways that give genuine insight about people’s social interactions.

OkTrends on what words in 1st messages are correlated with more/less replies:

OKTrends on how well various religious beliefs pair together on average:

OKTrends on why you should never pay for online dating (alas they pulled this one after being acquired by a commercial dating site, here it is as saved by others):

eHarmony claims over 20 million members on their homepage, and their CEO, Greg Waldorf, reiterates that number regularly in interviews1. If your goal is to find someone special, 20 million people is a lot of options—roughly a quarter of all singles in the U.S. This sounds awesome until you realize that most of these people can’t reply, because only paying customers are allowed to message.
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Remember, sites like Match and eHarmony are in business to get you to buy a monthly subscription. There’s nothing wrong with profit motive, but the particular way these sites have chosen to make money creates strange incentives for them.
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[T]he only way they don’t make money is to show subscribers to other subscribers. It’s the worst thing they can do for their business, because there’s no potential for new profit growth there.