Basically I want to say that I support this action (if I understood it correctly, based on IP addresses or whatever cdprojekt can pinpoint exactly who pirated the game over torrent sites). However, IIRC, european comitee of whatever banned even the theoretical possibility of providers controlling or spying on internet users!
Also note here that torrents, despite what ppl think, are not the primary pirating media. It's filesharing services (rapidshare, filefactory, megaupload, thousands of those) and I don't believe those sites will give away any data just like that as it'd be bad for business.
In the end I don't see CDprojekt will succeed in this effort at all. Instead, someone should make them another suggestion.
In my country there is a certain gaming portal and today they've brought the news that the game Serious Sam 3, if pirated, sometime the middle of the game, randomly, an unkillable frog appears and chases you all over the place, annoys you with it's pathetic damage but won't quit till you're dead. This was supposedly reported as a bug on the official SS3 site (dunno if all of it is true, I'm not playing it as I'm not into FPS genre), and then ppl discovered that it's not a bug but a "hidden feature", hehe
Anyway, who didn't bought SS3 but pirated it, got what he deserved. Either now they'll buy the game or will never pass the "deadly frog of doom". Even if that frog is removed by cracking the game, who guarantees there is not another unkillable butterfly later in the pirated game?
Now imagine if all who pirated The Witcher 2 were attacked by an unkillable drowner you just can't escape from in the middle of the game?
With that strategy against piracy, who needs DRM?
In any case, I've written in another thread, The Witcher 2 is not only one of the greatest games ever but also doesn't contain DRM (after patching it). And instead of supporting developers who didn't turn to lame Ubisoft schemes, ppl are pirating it. Unbelievable.
EDIT:
Sorry it's not a frog, it's a scorpion and there is a video of it:
http://www.youtube.com/watch?v=e91q5BtlxK0&feature=player_embedded