Keeping server logs is mandatory
John Gruber on his Daring Fireball Linked List asks:
The MPAA has taken over a popular BitTorrent tracking site, replacing the home page with a stunningly Orwellian piece of anti-bootlegging propaganda ("YOU CAN CLICK BUT YOU CAN'T HIDE.") Plus, they've obtained the server logs, presumably to determine individual users who used the site to bootleg copyrighted motion pictures. Question: Why in the world would a site like this keep logs?
Very simple: because they are obliged to, by law. In France, not keeping identifiable information on anyone who creates content on an online service is passible of a 75,000€ fine and/or one year of prison. It's actually a European directive, and I bet something like that exists in many, many other countries, including the US.