640GB ?
640GB is probably more storage than anyone will ever need.
Western Digital has begun churning out its dual-platter 640GB 3.5in Caviar SE16 hard drive in volume, the hard drive manufacturer said today, though buyers will be keener to hear when it'll ship drives with four or more platters. The desktop-oriented SE16 line currently runs to 750GB, the top-of-the-line drive being a model …
As a keen photographer who shoots raw files, plays back music, records TV using Vista Media Center, and streams it all to a Vista media center extender in the living room (Linksys DMA 2100), my primary hard disk fills 500GB no problem at all.
To back up the whole primary disk using Norton Ghost (or similar) you need ANOTHER 500GB, then ideally some more space (either disks or another HDD) for a 'files and folders' type backup.
If you want to stream HD movies from your PC, then you'll need even more storage space! Not to mention, the extra 10-20GB of photos every year....
etc. etc...