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.