The article below is about YouPorn.com (now ranked 35 on Alexa; ranked 51 when the article was written).
Revenue for it was $120,000 per month (I'd imagine the bandwidth expense eats up a huge chunk of that - maybe somebody here can do the approx calculations). These numbers quoted when trying to sell the tube site to Vivid for $20 million, so they're probably legit.
http://www.portfolio.com/culture-lif...nment-Profile#
Also from the article about pornotube:
"She explains that despite PornoTube’s 15 million monthly visitors, the website’s parent company, Adult Entertainment Broadcast Network, views it as a marketing expense, not a profit center."