I use YPN and must say the average click pay is not bad.
I think they still shadowed by Google and don't have wide enough advertiser base.

Also I realized many times they display ads not directly related to the content of the page which makes me wonder if:

- they don't have enough ads for certain niches or
- their's algorithm can not determine content of the page correctly

Sometimes I have to design pages especially for YPN to make sure theirs spider will see related text on the page before anything else...