No. Specifically iWork documents (plus a few other applications) can be synced, but you should not regard this as a form of backup since if a document is wrongly amended or deleted the change is synced to all devices. You should mantain additional backups.
The best local backup is to use Time Machine with an external hard disk: also cloning your hard disk regularly to an external disk gives you a bootable backup from which you can start up in an emergency.
You can back up reasonable amounts of data online by using third-party services such as Sugarsync and DropBox - more details here: