So I eventually got the shortlist down to Acer Revo, and Zotac MAG. Both are an Atom 330 (dual core + HT) device, Nvidia ION for graphics. Both (afaik) have 2G RAM, 160Gig HDD, WiFi, plenty of USB ports, S/PDIF out, HDMI, etc. so there was not much to choose between them. Acer Revo non-Windows version was impossible to find online, but Zotac MAG only comes with no OS. So the Zotac won.
On the front panel there's: Power Switch, (white) HDD LED, (blue) WiFi LED, USB 2.0, SDHC/MS/xD etc. Multi-card Reader, Mic, Phones/Audio Out, and also an extra USB 2.0 on the top.
On the rear panel there's: eSATA port, 4x USB 2.0, LAN, VGA, HDMI, S/PDIF Out, Power In.
First boot from an Ubuntu 10.04 Lucid Lynx beta on SDHC card worked faultlessly. So I used that to partition the HDD as: 2x 6Gig for 2 distros (allowing me to try 1 distro without affecting the current in use one), 4Gig swap, the rest for /home. Downloaded official final release version of 64bit Ubuntu 10.04 Lucid Lynx in the meantime, and then burned that to SDHC, booted, and installed.
So the Atom 330 really is dual core + HT, as evidenced by the System Monitor claiming there's 4 effective 1.6GHz CPU cores :)
First boot time clocked in at about 36 seconds :) (off to logged in, with auto login). Installation was 20 minutes (boot, type in user, passwd, hostname etc., install, reboot). Restart time after installing Nvidia drivers clocked in at 42sec.
XBMC was my Media Centre of choice. Installed it just by enabling repo and doing an apt-get. Works just nicely :) So far I've only enabled media sources from my main PC, but it plays really well. Oh and the current version also allows scrobbling to both last.fm and libre.fm :)
Optical audio out to the amp was not too tricky to sort. Had to enable digital audio (IEC something) in Ubuntu Sound Hardware settings (forget where), and then the same again in XBMC settings. And remember to switch amp to the right input channel ;)
Still to do:
1. get HDMI and plug in to telly (running VGA at the moment) [Update: now done]
2. sort out 1080p playback
3. work out what remote to use with it
