When it comes to backup expect the worst. In the old days we backed every thing up to Zip drives and then to tape.  We didn't know that a lightening strike hit our building and the backup tapes were are zapped and erased.  We found out only when trying to restore.

I backup continuously to Carbonite.  I do a separate weekly backup to Dropbox Professional and then a monthly backup to a portable hard drive.

Also note, backing up a computer is easy.  Restoring takes days to weeks (obviously restoring a file or two is easy and quick).  Some people are backing up to a portable SSD drive that could be used as the computer's hard drive.  But keep backups offsite.  What good is a backup in your office if the office burns down...........