Google AdSense provides powerful tracking and previewing tools to monitor and optimize the relevancy and targeting of the text-based ads on your Web pages.

The Google AdSense Preview Tool allows you to anticipate which Google Adsense ads will appear on your site, and to explore geotargeting differences (what ads will users in Malaysia see versus those seen by users in the UK) and possible alternative color combinations.

This is a great helping hand for heavy AdSense users, and coupled with the extended power of AdSense tracking channels is something to definitely learn more about.

Read more about it in my article about AdSense Channels and the Preview Tool.