One of my new year's projects is get a little MythTV Linux-based video box running under the TV. The plan is to get around 3TB of storage and rip all the DVDs and music in the house to it, toss in MAME for gaming, and use it as backup for all the family data, photos, etc. Then we'll get all the DVDs out of the tiny living room (they're already overflowing the shelves and crowding out our books) and into a storage box. What's more, we'll be able to find any video by doing a text search, instead of hoping that we can find it on the shelves (we alphabetized the videos last week and found three Blade Runners, each bought because the others had gone AWOL). Add DynDNS and a streaming server program and we'll be able to access our movies from anywhere in the flat or the world. Plus we'll run Miro on it and get all our video podcasts directly on the TV.
One thing I'd worried about was offsite backup, but I have an office a mile away that I'm also building a desktop Linux system for. My thinking now is that if I bought two 3TB boxes and synched them up initially, I could bring one to the office and use it as storage for my desktop system, and keep the two in synch with rsync over the Internet (our home DSL connection should be able to handle syncing up a new DVD or recorded TV show every day or two).
I even envision having an automated process that downsamples all our video into a format that plays on one of the cheap pocket video-players I bought in China (I even have one that's a watch!) so any time I'm leaving the house, I can just grab a couple episodes of something I'm following or a movie I've bought recently and toss it onto the device (and with network access, I'll be able to grab those shows from the road as well).
The thing I love about the idea of using NAS for this is that the big, noisy part of the system can live in a cupboard somewhere instead of right there under the TV. What's more, I can just pick it up and carry it to the office if the backup system blows up and needs to be resynched (or vice-versa). And with a separate storage box, I don't have to worry about finding a media center enclosure with a stupid number of drive bays. With 3TB of headroom, I don't have to worry about not having enough space to backup any of the working systems at home, either.