Isn't this kind of thread against forum rules?
Do nothing. Fighting piracy is a waste of time. It is must more in your interest to spend your time actively developing your skills.
+1 code faster than the pirates can keep up
We're having great success fighting it by providing extra features for verified licences (ie: automated updates). I've also seen great success in having a very prominent version number in the main graphics and item descriptions, and updating these as time goes on. People will be drawn towards new version 2.4 with extra features/fixes here on the marketplace, rather than downloading old buggy version 1.8 from a year ago.
There's also talk of spreading your own broken items to these evil sites. Items that simply don't work, half work or redirect to the real item purchase page after showing a nice message to the user.
+2 provide additional values which can't be pirated