For critical data, I want 3 copies minimum. Currently I use 2 (raid 5) NAS devices along with copies on 3 USB drives. The NAS devices synchronize each day and I run manual backups to the USB drives every other week. I use one of the 3 USB drives each time, cycling through the 3 drives. Off site backup is where I'm deficient. For small amounts of data a cloud copy is great. At the TB level and up my suggestion is an off site Hard drive copy.
I don't currently do this but I keep thinking it would be a good idea to keep at least 1 HD copy at a friend or family members house.
I do use google drive for smaller data collections like family pictures. With Picasa it's very easy to send copies to the Cloud.
Hopefully some of the smart people will comment... I'm not one of 'em.