As web designers, your focus can't remain strictly on aesthetics. Functionality must be the framework of whatever you produce. If you can't get your audience to do what you intended them to do, you need to go back to the drawing board. By the way, you should expect to go back to the drawing board, but have a plan! In order to understand how to improve your site layout and your design, you'll need data, and that's where heat maps and other user activity tracking tools can come in handy.
Heat maps allow you to track mouse movement, scrolling, and clicks to determine what areas of your layout are receiving the most attention. This can help you make intelligent decisions about the placement of items within your site. Never assume that just because you and your colleagues love the design and get how everything is related, that your audience will too.
There are a number of tools out there that track user activity in a number of different ways including heat maps. Most of them have some cost associated with them, but the benefit of knowing and understanding the behavior of your users could end up easily offsetting the price.
PT Engine: http://www.ptengine.com
Lucky Orange: http://www.luckyorange.com
Hey, who likes NOT spending a bunch of money to test this technology out? Google Analytics also has a heat map feature, but for those who are not overly web-savvy, the above choices may prove to be faster, simpler options.
Mind you, none of the data these tools provide are without flaws, but the insight they provide is a valuable addition to a web designer's arsenal.