exo : blah

You'll be wanting to follow this advice. Especially the bit about every night.

Although you may wish to cargo cult this incantation:

#!/bin/bash

# change $yourusername and name of drive accordingly
sudo rsync -axSE --delete \
--exclude-from /Users/$yourusername/backup_excludes.txt \
/ /Volumes/backup/

# required for the bootability apparently
# as it turns out this isn't at all required for booting. 
# the partition type in the jwz thing above are though.
# sudo bless -folder /Volumes/backup/System/Library/CoreServices

Where /Users/$yourusername/backup_excludes.txt looks a little something like this:

/tmp/*
/Network/*
/cores/*
*/.Trash
/afs/*
/automount/*
/private/tmp/*
/private/var/run/*
/private/var/spool/postfix/*
/private/var/vm/*
/Previous Systems.localized
.Spotlight-*/

One other tip is to exclude your backup drive from spotlight indexing otherwise you'll find when you want to eject it you can't as spotlight has its grubby little hands all over the damn thing. You can do this in System Preferences -> Spotlight -> Privacy.

When you smack your laptop down a bit hard and the death rattle starts emanating from your hard disk you will be mighty glad.

And really, every damn night or you will loose something you can't replace.