Here's my backup scheme. I'll start by saying I don't use my iMac in a manner that I'm creating files that are critical, so I don't utilize Time Machine. I have a 27" iMac 3.5 GHz i7 with 512 GB SSD. I then have two external drives, one a samsung 840 Pro 256 GB SSD connected via Thunderbolt via an adapter I put together, and then I have a 2 TB G-Raid USB 3 drive connected to my iMac as well.
I use Carbon Copy Cloner to make a Daily incremental backup to the Samsung 840 Pro SSD. I then use Carbon Copy Cloner to make a full weekly DMG file backup to the G-Raid USB 3 drive. I also have other folders on the G-Raid for all my Photo's, Movies, Important documents, etc.
Next, I use CrashPlan to backup all of my G-Raid drive to the Cloud. My theory behind the scheme is if there's a catastrophe and I loose everything at home, at the most I've lost 1 week of new data as I can resort to my CrashPlan backup and restore a new computer from the DMG file. If I loose an internal HD, I can boot to the external thunderbolt SSD and at max loose one days data. If I loose my external SSD, I can simply purchase another and immediately do another backup of the internal drive. If I loose the G-Raid, I can purchase another and restore from CrashPlan.
This probably wouldn't work for those of you that must limit loss to an hour or less, but for me, it works great. You've probably also noted that my external Thunderbolt SSD is smaller than my internal SSD, but I keep most of my data on the G-Raid and never plan on the internal drive getting over 200 GB in size. It's currently only 62 GB as I use symbolic links to my media on the G-Raid.
Jim