Even then it's hard to police, Best.
Is it illegal to buy a CD and loan it to a friend to listen to?
If possession of the physical CD can be "transferred" - why should an owner not be able to transfer an mp3. And by transferring I don't mean copying a cd or mp3 for a friend, but maintaining ownsership of both.
Again - as Best said - this law will be "on the books" - but only as an additional "charge." IE - if you're already suspect or have your computer siezed for other reason.
It's like getting Al Capone on tax evasion. If you get caught and have to pay fines for ripping MP3s - it will be because you've done something much bigger they've nabbed you on.
Before the seatbelt laws were fully on the books, you couldn't be pulled over JUST for that.
"A little nonsense now and then is relished by the wisest men" - Willy Wonka