Backing up is hard to do. OS X Time Machine makes it lots easier if you have a dedicated drive connected up to your Mac. But my main machine is a MacBook and I don't have a single workspace in the home where I can leave a hard drive ready to connect. I move around. Also not ready to spend the funds on any wireless backing up.
Second best (for me) is to turn Time Machine off and use on demand. I enable the TM status in my menu for this. Then connect the backup hard drive and choose "Back Up Now" from the menu. I try to do this every evening.??
I just bought a 750GB Western Digital My Book drive from Amazon (+-$100). The My Book includes Firewier 400 ports along with USB 2.0 and I need the FW for compatibility with some older computers (an Apple Cube for one). Not crazy about the look and feel of the My Book and??sometimes it won't mount immediately which I think has to do with its sleep mode. But I think it will do for the immediate future.
Time Machine is wonderful and restorable if your drive goes bad. It also keeps around old versions of files until you fill up your backup space. For that reason I backup my 150GB drive to a 230GB drive. TM will delete the oldest backup when the drive is full. You can also have it warn you before it deletes.
TM backups aren't bootable. If something goes wrong, you have to restore the backup. I want something bootable so if something goes wrong, I can reboot off the backup drive. SuperDuper ($27.95) accomplishes this and is very fast after the first full backup. It's been upgraded for Snow Leopard. I keep my Super Duper backup on a partition of the 750GB drive. It will only "grow" as big as the internal.
I use to use Carbon Copy Cloner by Mike Bombich and free. I switched to Super Duper because CCC was very slow even when only backing up changed files. I just visited Mr. Bombich's site and I'm curious if he's enhanced performance in the latest version. The site itself is much slicker than before and the ad blurbs make CCC sound pretty slick. I think I'll have to test it out.??
There is an excellent user-generated Time Machine FAQ over at the Apple Discussion boards. For one thing, it explained clearly how to move my old Time Machine backup from one disk to another under Leopard (Snow Leopard lets you simply drag-and-drop.)