Backing up

How do you back up? When I got my first computer, I would back up once a year onto CD-ROM, and then make weekly incremental backups (i.e. of any files newer than the last CD-ROM backup) onto floppy. (And all of the above would then be copied onto my work machine as an off-site backup, and once a year onto my father's, in case London got nuked, obviously.)

I still use the same system, albeit that it's now two 4.7Gb DVDs and a memory stick rather than a CD-ROM and floppy; but I've had a couple of people asking me why I don't just use an external hard drive. My answer is because my system works, because it allows me to easily consult old versions of differing ages, and because when taking my weekly backup in to work, a memory stick is a lot less weight to cycle with than an external hard drive. But I have no idea what other people are doing nowadays.

So, how do you back up? (And if the answer is "I don't", then start right now before something happens to your computer and you lose all your files, as has happened to several people I know.)