I'd personally say that's it's around 10-15%
Now.. this brings us to the real question behind this.
WHY oh WHY do people complain MORE about 1:10000 ccbill ratios compared to 1:2000 PPS 'inhouse' stats?
..why do people even compare the 2?
It's a whole different ballgame comparing 1stpage RAW to 2nd page uniques.. but, I guess it looks prettier when you show 2nd page hits..

..and it works, otherwise people wouldn't 'brag' about their 1:500 conversions.