The 2010 revenue of PlentyOfFish is USD 30 million.
IAC had bought OKCupid.
Free/freemium online dating sites like PlentyOfFish and OKCupid are only marketing tools useful to send prospective customers to paid online dating sites like Chemistry and eHarmony.
When free users got tired of free sites, they migrate to a paid one.
I estimate the 2010 revenue of OKCupid at USD 21 million (checking Alexa data)
OKcupid flawed article
"Why You Should Never Pay For Online Dating"