Great article by Ian Howie on Wordtracker’s site. We find many companies to a decent job of keyword search, a mediocre job of ad copy and a dismal effort at landing pages. However it’s one of the more important pieces of the conversion process.
If your landing page does not have anything to do with your keyword or ad copy or does not have a call to action, then it will be a wasted click. You are likely to see bounce rates off this page upwards of 85%.
Also Google assigns a quality rating to your keyword based on the quality of the landing page and its relevance to the particular keyword. The more targeted and relevant your ads and landing pages, the more favorably you are treated by Google.