I went the route of having NAS servers and a small Mini-ITX HTPC for each display. I wanted to be able to have a full PC experience on each display if I so desired. Plus, I feel a HTPC is the most flexible playback device as you can always update software or even view content through your web browser, regardless of what new services or formats are introduced!
For the NAS, I went with Synology. I got two DS411j units and put 4 3TB drives in each for a total of 24TB of storage. With both DS411j units connected to my dual-band Wifi-N Gigabit router, I can access anything stored on either NAS unit from any computer in the house. With proper formatting and software, I can also access files remotely via the internet.
Synology has many NAS units, including rack-mount units. I went with the DS411j for the simple reason that they are the least expensive 4-bay NAS units that Synology offers
Sadly, hard drives are still expensive at the moment. Cheapest 3TB drives I'm seeing are still up around $150-160. I got all eight of my drives when they were $120 a piece, so it wasn't too bad.
I backup my Blu-rays as full 1:1 ISO image files. I personally like to have the disc menus and special features (yes, even BD-Live) still available, so the simple 1:1 ISO files work perfectly for that. I also have HD-DVD backups - again, as 1:1 ISO files. I mention HD-DVD only because that informed my choice of playback software
To make the backups, I use Slysoft's AnyDVD HD. It is frequently updated for any and all of the latest copy protection schemes. AnyDVD HD does cost money for a subscription for the updates. I jumped on the lifetime subscription when it was cheap and available. Slysoft isn't offering the lifetime subscription option anymore, so it's potentially more expensive now, depending on how long you pay to keep it up to date.
Making the backups is extremely easy. I simply right-click on the AnyDVD HD tray icon and select "Rip to Image". I can select various options in the AnyDVD HD program for things like region code, forbidden playback controls, skipping trailers, removing BD-Live, etc. AnyDVD HD works for DVDs, Blu-rays, HD-DVDs and CDs, so it pretty much has you covered.
To play back the ISO image files, I first have to "mount" the ISO files so that the PC "thinks" I've inserted an actual disc into a disc drive. This is simple with Slysoft's free Virtual CloneDrive.
Now playback is identical to having inserted a physical disc. I use ArcSoft's TotalMedia Theatre 5 software since it is the only current software that still plays HD-DVDs!
To make playback look all pretty and organized, I use Windows Media Center in Windows 7. TMT5 integrates seemlessly for playback within WMC.
To get all the covers and metadata, I use MyMovies, which is mostly free with the option to pay for upgrades. Many people prefer MediaBrowser, which looks a bit more slick within WMC and is a bit easier for importing all of the covers and metadata since it simply looks at your folder names (you make a separate folder for each disc backup file when you rip them and then MediaBrowser looks them up on tmdb.com and pulls in the covers and data automatically). I prefer MyMovies though because MediaBrowser's data is more generic. For example, I have several "duplicate" titles for things like Watchmen or The Lord of the Rings, which are available in several versions. My Movies has a separate entry for each disc release, so you can have data and covers that are specific for the exact disc and it's easy to have multiple versions of the same movie. MediaBrowser's automatic data retrieval just goes by title - although you can manually enter titles, so there are still options with MediaBrowser. For me, MyMovies works, so I've stuck with it
For remote control, you just need a WMC remote, which will come with a little IR dongle that you plug into a USB port. If you want to be able to put the PC into hibernation rather than just sleep and be able to wake the PC from hibernation and not just sleep with the IR remote, you'll need to get a motherboard with a CIR connection option. ASRock is probably your best bet for such a motherboard.
I went with a HTPC for each display rather than a Popcorn Hour, Boxee Box or Dune for the simple reason that I also wanted a full PC and web experience available on every display in my home. All of those set top boxes are fine alternatives for playback. You'd just need a central Windows server to handle all the ripping and storage of the metadata and database. MyMovies works on Windows Server as well, so it's still a good option in that type of setup. Given how inexpensive it is to build a small ITX Core i3 Sandybridge HTPC though, I think it ends up being the better value. You get full HD-Audio and 3D playback support without any need for an additional graphics card and 24fps support as well. There are mini and micro-ATX options as well, many of which resemble a standard CE device sort of shape if you prefer.
