Each of the computers currently has a single solid state main drive and a raid 1 dual drive data array. I have a universal sysprepped base image of the OS, and then after initial configuration I take an image which I store to the data array. All the important documents live on the data array, which cross replicates to the 3 other computers and the network attached storage device, which also contains a raid 1 array. The really important non-confidential things also replicate to online storage.
At any given 24 hour point, the latest version of any document in my network exists on a minimum of 6 drive spindles, with 2 previous versions in the VSS cache. I don't grab anything off the OS partition except the user profile elelments, on the theory that if the OS destabilizes to the point I need to recover something from it I'm better off reloading anyways.
Pretty much the only thing that doesn't back up somewhere is the media PC DVR content, since it's just too big and not important enough.