I have a HP microserver setup with 4 drives in it at home. Two drives are mirrored and store my media, the other two are just single drives and are Time Machine targets for the macbook and mini. I also keep a bootable CarbonCopyCloner clone of the macbook offsite at work, just in case. For work, I have a locally attached Time Machine backup and bring home a bootable CCC image for offsite storage once a week. Dropbox I tend to use for current working documents, which kind of acts as an additional backup. I share a lot of documents this way though (work related), and have had a colleague delete files from the dropbox before, so I don't consider this a great backup strategy for me.
For DR, I would boot from the CCC image and clone it onto a fresh drive (assuming drive failure), or reinstall and use the Time Machine backup. Thankfully I haven't had to do this as of late, but I do check my CCC images are bootable about once a month.