In The Economist:
Once seen as the last resort for a bunch of lonely geeks, online-dating services have gradually shed much of the stigma formerly associated with them. 
Sounds great, but when there is money ($3-4 billion per year!) to be made, you take the chance unscrupulous people will exploit the lonely.
Last year Jetplace, an Australian company, admitted that it had been running more than 1,300 false profiles on a matchmaking service that it owned. Dating-site bosses maintain that such instances are rare, but detecting them can be tricky.
Obviously for some the risk is worth it.   You can't just walk down the street and spot fellow vampires to canoodle with (Vampire Passions) or Jews (JDate).

One thing all sites seem to agree on, regardless of cultural skew - hot girls sell: