Landing Pages
The book, Understanding User - Web Interactions Via Web Analytics, provides some information on KPI statistics, but this is an area that is really exploding as tracking and analysis gets better and better.
Every Second Counts: How Website Performance Impacts Shopper Behavior: Here is a good discussion of the effects of landing page load times, Every Second Counts: How Website Performance Impacts Shopper Behavior.
Landing Page Testing: How to test and what to test - The focus for landing pages is typically the experience of the user during those first couple of seconds when they hit the landing page. However, a critical aspect of land page is “how well are they designed for the search engine?”. Here is a nice article that highlights some of the key elements and the critical role of continual testing, Landing Page Testing: How to test and what to test.