In goes two 500 GB drives. I write dates on all my hardware to remind me when I got it - also give drives names - Kazumi from Shakugan no Shana.
Mac OS Leopard comes with a feature called Time Machine which makes backups of everything on your machine. Even if you change files on your Mac, Time Machine will keep the previous version up until the backup disk is full.
Do you keep backups of your data and how often do you back up? Do consider keeping an encrypted version of your data off site in case something happens to your house/apartment.
Macs are also great for making encrypted disk images too by using the Disk Utility application - find it in the applications folder.
