Downloading Mac OS X Lion is all very futuristic and convenient, but when your hard disk stops spinning and needs replacing, there's no option to boot from the cloud. While older OSs could boot from the system disks, Lion's download policy meant that you'd have to install Snow Leopard, then use that to go and redownload Lion. Boring, impractical, and neither futuristic nor convenient.
Problem solved, though – Apple's Recovery Disk Assistant, available to download right now, lets you reboot from a USB stick. You'll need 1GB of space. On that fateful day when the drive fails, hit the Apple key while you boot, crank out the Disk Utility, re-install Lion, restore a Time Machine back up and you're back in the game.
If all that still feels too risky, you can buy Mac OS X Lion on a USB stick directly from Apple for a steeply marked-up £55 later this month. But we think you'll find a 1GB USB stick comes cheaper than that.