WOW... although totally un-necessary that would be awesome!
I DARE someone to fill up a 4TB drive.
Of course thats what used to be said about 4gb drives too
From what I understand of Time Machine, that might be quite possible. Since it is taking hourly, daily and weekly snapshots of any files that are altered on your system, I can see scenarios where this could result in massive storage requirements. In particular
-iMovie / iDVD. Large video files that are being cropped / edited, or iDVD projects which are being worked on, could result in GB of backup every hour
-VMWare Fusion Virtual Machines. I'm likely to have around 10 of them running on my Mac at any time (dev studio, SQL box, web/application server, domain controllers, clients) and each is a 10 GB machine. They are constantly changing, so every hour Time Machine would want to take a 100 GB backup. That is 2.4 TB over 24 hours !!
Of course, I'll have to tell Time Machine to skip my VMs for now, since my 500 GB external backup drive would last all of 12 hours....
Not so sure about iMovie / iDVD projects ?