Targeting by site is too broad. How about targeting by site subcategories?
I am slowly, painstakingly testing YPN on carefully selected pages on my music site (only on pages where Adsense performs poorly). So far:
Using Ad Targeting (matching ad categories to specific page URLs), I am observing good ad relevancy in several areas (radio, event tickets, consumer electronics).
Using Contextual Matching, I am seeing too many (unblockable) florist, phone, and other RON ads for me to use it seriously anywhere. In my niche for my test pages, contextual ad matching is too hit or miss.
In general, I am thus far unimpressed with YPN ad matching. It probably has more to do with a limited supply of ad inventory than with any deficiency in their ad matching technology.
Compared to Adsense, YPN requires more micromanagement to achieve decent ad targeting. Hopefully, as more advertisers sign up with YPN, and when and if they sort out this RON ad filtering confusion, YPN will require less work to make widespread use of it worthwhile and effective.