I had done a review on Adgridwork, the free ad network, a few posts back. And this is what running the ad on this site for one month has brought.
515 Site Requests - # of page views the adblock on your sites recieved.
9,526 Impressions - # of times your ads appeared on others pages
4 Conversions - # of times your ads been clicked on another users site
16 Clicks - # of times someones clicked the ad on your site
0.04 % CTR - conversions relative to impressions
Now this was when this site didnt get even close to the traffic it currently recieves and for the great value of $0 cpc its definently worth displaying on your site. I also ran adgridwork on a few of my other ads and with decent ad copy they all got about 1 conversion per 150 site requests. You can run adgridwork with every ad network so unless you dont want free quality traffic I dont see why anyone wouldn’t use them.
I’ve tried adgridwork before but I put it down because it resembled google adsense too much and simply wasn’t bringing in enough traffic.