MobileMe: Backing up files that are stored on your iDisk
Summary
Your MobileMe iDisk is a convenient place to store and access files from anywhere. However, as with any important files, it is a good idea to keep backup copies of your files on more than one disk.
Products Affected
MobileMe iDisk
If the only copy of an important file exists in a single storage location (such as only on iDisk or only on an external drive), and you accidentally delete the file or have second thoughts about the changes you saved, you may not be able to restore or recover the file.
If you store an important file on your iDisk, be sure to keep an up-to-date copy somewhere local, such as on your computer's hard drive (your desktop, for example), or burned to a CD or DVD. You can use Time Machine with an external disk in Mac OS X 10.5, or many other methods to back up your important files in Mac OS X.
Additional Information
For even greater peace of mind, you can save different versions of important files with slightly different names via Save As. For example: My Great American Novel.pages, My Great American Novel-rev1.pages, and My Great American Novel-rev2.pages.
For more information about how to back up your MobileMe data, see this article.