I have been using kontera for last 2 months roughly and its working pretty well than I have expected. Initially, I have read somewhere, that adding kontera to your google site/blog reduces your click through rate and earnings in general..but frankly speaking, I have not noticed that big a difference..may be I don't have that much of traffic clicking on kontera thats why..but do go for it..its quite better than even bidvertiser..coz even one click can earn you $X..depending upon your blog content..