An interesting thread to bump in to as I was having a discussion on exactly this subject only yesterday evening; I currently have about 400Gb (and growing) of audio visual media and can't find a usable, reliable, cost effective offsite (broadband upload) backup service that I'm prepared to invest in.
My idea is therefore to place a 1TB NAS in the home garage roof space (normal apex style) where it is unlikely to be a theft target and unlikely to be destroyed if the house burns down (it's a separate building). Connection would be "ethernet adaptor in to mains cable in to ethernet adaptor" (I haven't checked the proper term to use) from my hub, since the garage is outside the range of wireless connection.
My techie friend agreed that this will work, and allayed my fears about winter temperatures and humidy if I place the NAS in a box with no floor (just a support rack) to allow heat to build up and then the excess to spill out from the bottom. Summer heat shouldn't be an issue.
He also pointed me in the direction of making my own Linux NAS, having successfully done so himself (including the ability to quietly get on and do some BitTorrent downloading without needing a PC to be running, though I don't need this feature)