Mac backup
As everyone who has the latest Apple OS (Leopard) knows, they’ve included a backup solution called Time Machine. This really can be a life saver - I’ve found it particularly useful when installs go wrong, you can have the machine back the way it was in about 15 minutes - rather than a painful and lengthy un-install/ re-install process.

There has been reams of text written about the best way to backup -
lIfehacker has abundant and very good guides on this.

In addition to Time Machine I use
SuperDuper which creates a complete boot-able backup which mans if your main drive fails you can be back at work in the time it takes to reboot. Their support is excellent too. The Leopard version fixed one of the faults of the previous version in that you don’t have to be logged into the main account for the process to kick off automatically.

I also use
mozy which provide and off-site backup, although I’ve never had to use this in anger - this is a fire, flood theft kind of a thing. The advantage of tis is that it’s a relatively cheap way to backup off site (approx $5/ £2.50) a month. The disadvantage is that the initial backup soaks up your bandwidth and is very slow on an ADSL line.

Hopefully I’ll never have to use the full backups but best to be prepared (belt and braces and all that).