When I ran MegaOrg's network (1800+ PCs), we had a few people who didn't just keep every e-mail they ever received. They also printed out every single e-mail they ever received (including "Hi, going for lunch"), and filed the paper copies. If these people ever lost a .PST file from four years back in a disk crash (we limited backed-up network drive space, so people would hoard their precious old e-mails in a .PST on their PC's hard drive), it was as if they'd lost a limb.