Compete.com has just released a monthly index of the top 200 sites in the USA ranked by what seems like user minutes spent on the site per month. Plentyoffish comes in at #73 and the only one person website on the list 
http://blog.compete.com/2007/02/05/compete-attention-200/
This is a very important ranking system for dating sites because if users don’t spend time on dating sites they can’t start any relationships.
I also can’t see how anyone is going to pay for hitwise or comscore data. Between Quantcast and Compete there is more free data out there then you can get from these paid sites.
