OK, some feedback.
Ordered 2 of these boxes last week before I knew I could get them from Postmanpat. From now on will buy from him.
1st one set up as a dedicated NAS with 4x2TB drives running unRAID.
2nd one was to experiment with as a XBMC player and here the fun and games started with finding the correct graphics card that's low profile, draws less than 25W, fits into the space available and is as powerful as possible.
Eventually bought a Sapphire 6450 1GB (LP, passively cooled, fits easily but no LP bracket) as I could not find a Nvidia card (either a 210 or 520). Just as I got home today at 5, Jacques from ACT Link phoned to say he got me a MSi N520GT and even brought it over to my house. Owe him one. The card is actively cooled, fits perfectly and comes with a LP bracket. All lekker.
Installed the card, 4GB of RAM, removed all the hard-drives and installed XBMCLive to a small USB stick plugged directly into the Mobo.
First problem; XBMCLive does not know the 520.

Download the 520 Linux drivers from Nvidia, install and now HDMI video works fine.
Second problem; No audio.

Fiddle a bit, but not much. Give up, too much red wine by now.
Download and install generic openelec onto another USB stick and it all works 'out-of-the-box'. So, right now, I'm using openelec and it's looking good.
Playing the reference 1080p 264 Avatar shows slight issues with playback but not so much that I want to slit my wrists.
If I can find one of my Win-7 disks, I'll install Win-7 onto the internal drive and test like that, but right now I'll test for a while as a clean openelec install.
I'll probably convert this to another NAS at some point and build a more powerful, dedicated XBMC player.