And then there's the Internet Archive. IANAL but it seems as if there's effectively this assumption that opt-out makes everything OK even if there's not much if any legal basis to it. (I wrote this piece back in 2005 and not a whole lot has changed: http://bitmason.blogspot.com/2005/07/thoughts-on-wayback-mac...)

To be clear, this is arguably the way that the Web almost has to work--but that doesn't make it all neatly legal under current copyright law.