it is a very difficult problem to tackle. Past solutions have been fairly unsuccessful. However, cd-keys, online accounts, and other such things have been effective at the expense of a hassle ofr the user.The only "solution" (if you could really call it that) is bandwidth capping, which is incredibly draconian given the fact that it can't discriminate between legal and illegal downloading/uploading. It's about on par with the current state of DRM with computer games. This is why we are seeing a shift towards ISP's being the new front on this ongoing battle.
this is outlined under something called "fair use". Wiki has a decent page on it.What about making a copy of a CD and giving it to a friend? What about lending your CD to a friend? What about recording movies off television so that you don't have to buy the DVD's? To what extent is that acceptable? Where is this line you are drawing, and how exactly is it not arbitrary?