It's astonishingh how many people are not ware that copyright law also applies in cyberspace, or pretend they do not know. I Google excerpts from every post I publish like raincoaster does. I use copyscape http://copyscape.com/ to search for copies of my posts on the web.
When my posts are stolen and I find them on a monetized blog I do a whois seach and contact the site owner where possible (one of the caharacteristics of splogs is lack of contact information). If I do contact them and they mess with me rather than immediately removing my content. I bring the hammer down hard. I do as advised above and report the site to Google Adsense and to all other advertisers on the site first.
Then I send in a DMCA complaint to the web host. I too have a copy and paste on hand.
Next I publish a blog post identifying the splogger and post the whois information in it and state how disgusting content thieves are. My readers and I decimate them and we post to all social networks and forums we belong to warning others of their slimy behavior. We report the splogger to every social network they have joined to as the social networks all have copyright provisions in their ToS and content theft is breach one is banned for.
The thieves always take my content down and most beg me to remove my posts and my forum postings on social networks too - fat chance! Those who blog for bucks are in business and practicing due diligence comes with that territory.
However, in the case of a newbie blogger with a non-monetized blog who has yet to educate themselves on copyright I have been known to be forgiving. If I contact theme and they immediately say they are sorry and remove the content then that's not a barrier to securing my friendship.