The old Shuttle HTPC which had a troubled life finally died a week or so ago (no longer recognised the boot disk.)
I've finally settled on its replacement, detailed in this post in the forums of an enthusiastic Australian HTPC community. Don't be fooled by the Windows branding all over it - Linux gets quite a fair dealing in there and I've been given a lot of good advice regarding mythtv (using mythbuntu) and XBMC.
As a bonus, the new hardware is almost half the price of the old. Way under $1000. It'll be more future-proof and repairable (being standard components). And it'll look nicer too.
ps. never, ever buy a Shuttle unless it's covered by a really good warranty with full replacement.