MobileMe: About enabling read/write access to your iDisk Public folder

If you choose to enable read/write access to your iDisk Public folder, it means anyone can add to, change, or delete items in that folder. If you have important items in your Public folder, make sure that you either have or make a backup copy. You can also limit access to your Public folder by password protecting it. However, anyone with the password will still be able to make changes if you enable read/write access. 

If you need to enable read/write access to your Public folder, even if it is password protected, it is recommended that you keep a copy of any important data in a safe place so that if someone else deletes or changes your files, you still have a copy. Place your backup on a volume other than your iDisk, such as an external hard drive or burnable disc, or use Time Machine.