Using CD-RW for email files

A manager currently uses a 100MB zip drive to hold his email folders and is adament about keeping his mail on removable media which he carries back and forth from his home and work computers. He now finds 100mb insufficient and wants to increase the capacity to 750MB zip. Rather than buying 2 new zip drives, I would like to switch him over to CD-RWs which he currently has in both computers. Can you think of any problems if the CDs are created in the proper format?