I have 31TB of ripped movies on my upstairs server. This is not my entire collection, but it does include all of my blu-rays and some of my favorite DVDs. These are ripped to ISO, MKV, or folders depending on the origin of the content and whether it is a tV series or not (I like TV episodes in MKV format). I use MyMovies as the database. This works with Windows Media Center to ensure that I have cover art and metadata for each movie in my collection and presents a nice interface inside Windows Media Center.
I have two home theater PCs, one upsides and one downstairs. Both use the MyMovies software to keep the database which provides the back end to Windows Media Center. Both HTPCs can get to the movie server upstairs via my gigabit network, so I can play any of my movies from these PCs. These PCs send an video/audio signal over HDMI to an AV receiver I have at each location. These are the center of my home theaters and they both have at least 5.1 speaker systems and a HDTV for viewing.
The MyMovies folks have apps that work on both iPhone & iPad, as well as Android devices. So, with these apps, I can control my systems inside Windows Media Center. That means I can call up a movie to watch with the app, and then play it. I can read all kind of info about the movie as well as view trailers and such. I can control playback on my HTPC from within the app, as it has a remote control feature. It works over your wifi network. All in all, pretty cool. I think this is on-topic with the question asked by the OP, though, obviously not everyone is going to have 31GB of storage on a PC sitting around. ONce the prices of HDDs start dropping again, I will start expanding my TB (I actually have even more TBs sitting in here that are not in use yet -- just holding for hard times like now).
The error is because my HTPC is in sleep mode now and I'm not using Media Center. It goes away when I'm actually using the HTPC.