Google themselves have actually gone on and approved of this. For anyone sitting on an empty domain, paying the yearly fee and having nothing but dreams of what giant business you’ll build on it can get old. Google’s gone and offered to help out with parked domains using AdSense.
For anyone who isn’t completely sure what AdSense is, Google AdSense is one of the easiest ways to put advertisements on your site. You sign up, set up your ad banner specifications, then place the code where you’d like the ads to appear in your site. You earn money for every click a visitor to your site administers to the ads you’ve placed.
However, it isn’t all perfect – Google gets rather upset if you put AdSense on your site and then click on it many times yourself or have your friends do it. Repeated clicks from the same source will flag a warning to them, and they can ban you from AdSense. Permanently.
That, and any time someone clicks an ad, sure you earn money, but you also lose your visitor. They’ve gone off somewhere else, and you’ve lost that potential client/customer. Some people are fine with this, thinking that if the person clicked an ad they were leaving anyway – but there are often instances where an ad catches the eye of a visitor who would otherwise have spent more time on your site. If you don’t want to distract your visitors from your own site content, I’d recommend minimizing your ads, be it through AdSense or otherwise.
However – having a domain that is unused is not going to lose you any visitors to a quality site. So why not earn money through it? If you have some domains that you’re not using and want to earn a bit of money from them, you can check out Google’s domain parking AdSense option. As it IS Google, they’ll walk you through the how’s and to’s of everything, it’s pretty straightforward.