After testing YPN for the past several months, very selectively at first, then more aggressively (after I implemented foreign-traffic filtering), I have finally decided to abandon using YPN for now.
The CTR, on two different sites, is just too low to be worth my while.
Ad targeting continues to be poor to middling. Where ad targeting is okay, it tends to be repetitive, with the same on-target ads appearing on page after page.
Moreover, Adsense link units work best on my sites. YPN doesn't yet offer link units.
But I have no regrets. Working with YPN motivated me to adopt techniques for filtering non-US visitor traffic. I now employ these techniques, for example, to serve Amazon.com USA ads to US visitors, and Adsense ads to foreign visitors. I also now do ad rotation everywhere on all of my sites.
So, it's been a useful learning experience if nothing else.
Good luck to all of you still actively participating in the beta program. I'll continue to check this forum from time to time to see if things improve, particularly the ad targeting, ad selection, and overall CTRs.