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If a webmaster copies you, first email him.
If he don't answer or don't wants to get off the copied content, and uses Adsense, you can email Google about this.
If someone copies you and emails Google telling you are the copyright violatior, Google will investigate to know who is telling the truth, sure.
I contacted Godaddy (his web host) and gave them the URLs of the copied pages on his site and the URLs of the original pages on my site. They sent me an email back telling me to fill out a formal DMCA complaint. I did, and over a week later the pages are still up. Godaddy says without proof of a copyright filing they won't remove my pages from his site.
I contacted AdSense support and the AdSense was disabled from showing on his entire site within hours (both my AdSense code and his). The next day his site disappeared from the Google SERPS and his Toobar PR on the homepage went from 4 to 0.
Complaining to Google does work...
Copying your site is bad enough, copying your site including your adsense publisher's ID is a double whammy, especially if you are earning significant monies from the program. It's just too high of a risk.