Guys, if the sites that are ripping off your content have Google Adsense, then you might want to contact Google, too. They have strict TOS about their ads being put on pages that don't have original content.
There are two benefits to this:
a.) The thieves may get their Adsense account banned (hehehe – I would wish that on anyone except those folks who do nothing but steal content from others)
b.) It established that you are the owner of said material, so that if Google ever notices duplicate material YOUR account won't get banned for it… The Adsense folks (computers?) are extremely trigger happy and it is almost impossible to get a banned account back if they shut you down – even if it was unjust.