I have seen wild fluctuations in my CB sales over some period of time now. I do believe that there is something fishy going on but it is hard to prove. Needles to say, I have since moved on. With all of the negative posts on this forum and others, CB has surely lost a lot of affiliates.
Clickbank is great but what i suggest is first you research on all the ways you will market your affiliate links. There are many products and many websites like clickbank so finding a product or service to sell is actually the easy part. Actually making sales is another thing. Hence for me, researching on marketing a product is more important as that is what is define your success.