I am a huge fan of Jamie Zawinski's style of doing backups (which basically means you make a full copy of you disk every night and in case disk dies you replace it with identical in no time).
There is one small implementation problem with this approach though: our disks grew tremendously in last years, and did not speed up too much to compensate size growth, which means making a full copy of even a laptop drive could take a lot of time (and no, using rsync as JWZ recommends is not an option, as you still have to deal with partition table, boot sector, LVM and $DEITY knows what else).
It wouldn't be that bad if full SATA speed could be achieved, but eSATA enclosures are still a bit expensive, so I hook up my backup drive using USB, which is much slower.
In order to make the backup a bit faster I scratched a small utility called brdrsync which reads the both disks' contents, compares it and only writes back to backup drive those sectors which are changed since last backup. Really helps. Not sure why.