Website Magazine has an article about Google Labs new tool that will show the portions of your Web page most visible by the average user.

Browser Size overlays a map of sorts, showing percentages of typical users and what they will see on your page ... It provides a nice snapshot so you can see if the most important parts of your page - calls to action - are being seen immediately by the average Web surfer.

Your can read the whole article (New Google Tool Tests Your Page for Calls to Action) Here

hth ~megan