i recently got rid of a bunch of old machines. now i only have 3:

primary machine: laptop running arch (but i think im ready to move to crux) and a few other testing os's in a vm's.
programming, web-browsing, chat, i do almost everything on this machine. i back it up about once a month. i have a folder structure i try and adhere to so that backups are just a simple shell script that pushes stuff to my nas.

secondary machine: nas / htpc running arch. this is a mini-itx mobo with 6 500gb raid 10 hard drives and 6gb of ram in a small box sitting on my entertainment center. i use it as a file/backup server, and entertainment. it runs kodi (xbmc) for tv shows and movies and a bunch of emulators for retro gaming. it's also tied into my seedbox and automatically syncs files and tells me i got new stuff to watch when i login next time. whole thing is controlled via a boxee box remote (w/ the keyboard on the other side). i also have another boxee box in my bedroom that i stream video from the nas to. the only backup it has is raid 10.

tertiary machine: old laptop with the guts ripped out of the case and wall mounted. it's sequestered from the network (by physical means and mac address). i only use this thing for weird tests (read malware analysis) i dont want to do on my real boxes or on the network.

i also have many vps/seedbox servers in "the cloud".