Time Machine is Apple's backup utility included in Mac OS X Leopard. It has a straight forward setup and automatically works. Still, there are several tips I found on the web while searching a way to move my old Time Machine backup from an external hard-drive to my new drobo. I found 2 blog posts that are quite useful.
1. From Ryan Block's blog: a tip to save some space on your Time Machine drive. By default, Time Machine backs up everything on you Mac. There is an option to exclude certain folders/drives, and Ryan has a list of certain things that Time Machine can skip to save some space, things that are easily recoverable from other sources.
2. From Stephen Foskett's blog: Time Machine is great, but what if you want to upgrade your Time Machine drive to a newer/larger drive? There is an option to change disk in system preferences, but it doesn't move your old backup. This tip uses Disk Utility to "restore" the old Time Machine drive to the new one. One note, make sure you don't need anything on the new drive, since I can only make this work if I check Erase Destination option.