Mac users, there is no reason NOT to set up Time Machine on your Macintosh. This feature, added with Mac OS 10.5 backs up your entire Mac -- data, applications, settings -- and then updates any changed files on an hourly basis. All it takes a an external hard drive (I usually recommend on about 250GB in size). Theses drives are on sale all the time for prices around $50. This is a great investment to give you substantial peace of mind about your Mac.
While Apple touts the ability to easily restore deleted or damaged files using Time Machine, my use of the software has almost always been to restore a Mac that has crashed or build a new Mac that looks exactly like and old Mac -- including email, settings, desktop pattern, printer, everything!
I had a client who happened to get a lemon iMac. The unit died after 2 weeks, but we had set up time Machine from the very beginning. It had taken several hours to move data from her Windows machine and set the Mac up the way she wanted it and all that would have been lost if we didn't have a Time Machine backup. Instead, we were able to plug her backup drive into the new Mac, select "Restore from Time Machine Backup" during the setup and about 15 minutes later she was working again -- with all her original settings.
I recently had to replace my Time Machine backup drive, as I was using an older, leftover drive I had lying around the office. I found this Seagate FreeAgent Go drive (250GB) on sale at a local retailer. I like it, as it is small, quiet and requires no external power cable. It is powered directly from USb port of the computer.
Mac Users -- if you haven't set up Time Machine on your mac -- DO IT TODAY! You have nothing to lose and everything to gain -- including peace of mind.