Adsense is popular among web developers and bloggers as an ad serving application. Most of us use it, and without a doubt adsense is the most popular of all ad serving applications. So here are a list of adsense forums where most of your questions about adsense can be answered.
http://forums.digitalpoint.com/ - a useful forums for web gurus and beginners alike. It tackles a lot of web topics including adsense
http://forums.seo.ph/ - mostly used by Filipinos, but still useful for everyone