With clickbank I have better luck with a landing page pre sell first. I usually go opt in page-presell page-sales page of product. That works well for me.
I've tried direct linking and got sales, but not as many as with the above setup.
Little late, but preselling is definitely the key to success. I don't think one very successful IM'er just simply direct links to offers. Even if you don't have a landing page, at least get their email then send them to the product page. A large email list = $$$$