For those readers truly new to it, let me point out Google's escalating plan, some say, to wipe out affiliate marketers. The first measure was to display only one ad per page for a given destination, only the top bidder's direct link ad will get displayed on a given page.
Google's added-on landing page/ad quality score system (which allows them to reg the competitive bid pricing system) puts advertisers at the mercy of the quality of the product landing page quality, certain squeeze pages or long form sales letters don't rank well in their quality score system.
You can address both of these issues by creating an internmediate landing page, for best quality score, some create a differently worded landing page for each different ad group.
Quality score is a huge issue (with google) some big budget ppc gurus report top position ads paying 1/10 the amount the last position ad pays, benefiting both in cost and ad position by providing their viewers a better shopping experience.