Google AdSense is a great CPC program that lets regular webmaster joes like levik and I tap into the revenue that Google collects from displaying its sponsored links. You display the Google sponsored links on your site and for that, Google AdSense will pay you for every clickthrough. Rates vary depending on your website's content and the price-per-click of campaigns that Google will serve on your site, but generally, their eCPM is comparable to Tier 1 ad-networks, albeit more volatile. AdSense will mail you a check everytime you reach at least $100 in your account.

The beautiful part is that Google will serve you the targeted links -- links that are usually relevant to your site's content. It can lead to more revenue for you, but it can also mean that you will be sometimes displaying the link ads of your competitors. However, AdSense has a nifty URL filter tool that takes care of that problem -- you can enter up to 200 competitor URLs into the URL filter and AdSense will not serve them on your site.

AdSense arranges the sponsored links in many available ad formats -- 468x60 Banner, 120x600 Skyscraper, 728x90 Leaderboard, a number of rectangle sizes (including the popular 300x250 medium rectangle) and a 125x125 "button". Depending on which size you pick, Google will show from one to five ads inside the creative unit. You get to fully customize the appearance of the ads above -- AdSense created an easy to use customization tool that already has about 25 canned color palletes and lets you create and save your own.

Depending on your target audience you may benefit from either making the ads blend in with your overall site design, or making them stand out. Because this is a strictly CPC program you will want to make sure people can see and click the ads, so placing them at the very bottom of the pages will not yield good results - these units do the best embedded right in the middle of the content.

Some time ago, Google introduced image ads for the more popular media sizes as well. These get served one per ad unit, and can be opted out of. Other revenue-generated formats that are a part of Google AdSense are: a simple link unit and AdSense for search. A link unit consists of a few related links, no descriptions. Clicking on a link in a unit takes a visitor to a page of related ads. AdSense for search is basically an embedded Google search field - webmasters earn money from users clicking on sponsored links on the results page.

Their reporting system is beautiful: you can create up to 200 "channels" for every ad or for every page that Google AdSense ads run on. On the admin portal itself, you can create one-click custom reports or choose from an array of canned reports already available.

Unfortunately, you still have no control over what campaigns are served to your visitors and cannot see the price-per-click-per-campaign report. But hey - this disadvantage is greatly outweighed by the ad network's benefits described above. Since its inception, AdSense's format has been copied by other ad networks, most notable of which is YPN (Yahoo!Publisher Network). However, webmasters who had a chance to test both report that AdSense's eCPM exceeds earnings from YPN. So, until further notice - stick to AdSense.

In the application process, Google AdSense has been known to discriminate against sites that display excessive pop-ups. The excessiveness is judged solely by AdSense and we know of instances when webmasters got rejected simply because they displayed a pop-up or two on their sites. The lesson to be learned here is that you should remove pop-ups from your site, when you submit your application to join Google AdSense. Don't worry, you can reinstate them -- after you get accepted.