I backup entire disks using a towers of hanoi algorithm with (wait for it...) good old dump(8) to a second local hard drive. This method keeps 7 full days of backups (using an incremental diff, so it's fairly space efficient). I've used this method for almost 15 years and have used it dozens of times to recover missing things. dump has never failed me!

On my other servers I use rsync just to keep a current mirror around. I always ask myself, "How hard would this be to recover if I lost it?" and "Will I need to go back in time for some things?" Depending on the answer to those questions I make my backup strategy for the server in question.

Yesterday's Daring Fireball post on the same topic said it best: "Every hard drive in the world will eventually fail. Assume that yours are all on the cusp of failure at all times. It’s good to be spooked about how long your hard drives will last."