I'm becoming a big fan of the "YPN + Chitika on the same page" approach. I think what's happening is that, when YPN can't or doesn't serve a highly targeted ad, Chitika is an attractive alternative to visitors. The trick is to take the time to come up with a few specific kw's to use in the Chitika code for that page's content. Don't get lazy and use a default set of kw's that only pertain to the general theme of your site. My Chitika income continues to rise as I add it to more pages that have YPN on them. Just as important, I'm not seeing any decline in YPN income (in fact, it's rising).