I just reread this thread and noticed your post about restricting our right to make backups. That is a good point. But this is the problem with electronic technology, that backup can be distributed and who the hell is going to find out. If you make it copyable, then it is copyable for everyone, causing piracy. I can only think of one method that might work, although it's not entirely enticing or plausable yet:
Online serial number authentication. You cannot start the game until you log on and your serial number is authenticated, similar to Neverwinter Nights. Should yor serial number be used more than once simultaniously, alarm bells ring. This idea is based on the design of DNS security. This is looking at a time where all machines are permanently connected to the 'Net.
And even then, how long before people produce fake authentication proxies...
