OkCupid.com's pretty good about it. Maybe I'm biased.

Also, dating sites aren't the only sites susceptible to spam. Craigslist would probably be a spammer's heaven if they didn't have such great community filtering features.

You're right, Craigslist is a good example. But even there there's enough phishing going on that I'm not comfortable using the dating section. I've had success finding apartments though.

The difference with dating sites, though, is that they only work when members are active, aggressive, and open with their personal information. They work best in a way that spammers will rush to exploit, at which point everyone gets frustrated and stops using the service. This doesn't stop spammers, and pretty soon the ratio of valid profiles to fake ones is ridiculously small.

More importantly, Craigslist uses pay to filter spam in other ways: real estate and job listings.

In that case, it was "asked" for by the users.

plentyofish.com apparently does a pretty good job.