Backing up in the sense of maintaining a full copy of your harddisk seems increasingly unnecessary these days. Most of the stuff I would care about losing is effectively already backed up on Github, webmail, Facebook, Steam, etc.
I don't think that counts as "backed up". Personally, I always try to make sure I have a mirrored copy of any of my data that I store with a third party, unless I feel comfortable with that data vanishing without warning.
He's got the point though that only one's data needs to be backed up, not every single bit on the disk.
That depends what you're trying to achieve. With a full disk clone you can lose a drive and be back up and running in minutes.