I've installed 12.04 on mine. I did it due to longer support and stability.
My setup is similar to yours, except the sound card, I will use the HDMI output for that.
What I looked in with this server was to have NAS and Media Center functions in one box. And the main reason was, of course, price. I bought this box for 160€, this is cheaper than most 2-bay NAS on the market.
Installation should be pretty straight forward. Aside from the AMD proprietary drivers, a normal install should be anything you need to put your machine to work.
I haven't dwelled much into the configuration of the machine, but here are my notes.
- Rhythmbox: Since I moved my music library to the server I tough that was no sense in having a samba share just to sync my iPod in my Windows machine. This worked perfectly, even allowing me to use different folders for Podcasts and Music.
- XBMC: Just touch the surface here, but it seems that XBMC is a really good way to have your media library organized.
- Sensors: It seems that I can only check the temperature of the CPU, and not each individual core. Memory temp is allowed, but chipset temp is not present.
- X: Even in Unity 2D the X process takes quite a toll on the CPU, can't understand why.
- ATI driver: It seems that nVidia drivers have a better support for hardware decoding features that allow better performance while playing videos. Note that this is just a empiric guess, I have no proof that this is true.
- Remote Administration: I've checked Zentyal. Although it is it's own distro, since it's based in Ubuntu it seems that you can install it easily using Ubuntu repos.
- Input devices: Haven't checked if wireless keyboards or pointers work with Ubuntu, but a quick search on Google should provide more info on this.
I'm still exploring, but seems to me that maybe the best course of action is to just install something like OpenMediaVault or FreeNas, and have another device just for media decoding.