I stopped using CoinURL a month or so ago, since I was getting paid 0.00000600-0.00001200 BTC per click, which was really terrible compared to other advertising services.
Has the CPC gotten any better to reconsider using CoinURL?
PPC should be based on how much the advertiser paid for the click. This means it will (or at least should) fluctuate a lot from day to day, much like it does with AdSense.