The SheevaPlug eventually turned up on Monday (this is a VERY popular item right now, and leadtimes are very long).
Anyway, I'm REALLY
impressed with it so far. It's an incredible bit of kit for $99. It's pretty simple to get Twonkymedia running on the plug, and it performs very well.
I have detailed setting up Twonkymedia on the plug, on the plugcomputer.org Wiki.http://www.openplug.org/plugwiki/index.php/TwonkyMedia
The plug is running other stuff nicely, lighttpd web server (with PHP), samba windows filesharing. and I have some other plans for it too. I'm currently using 30% of the space in the flash, which includes the Ubunut 220.127.116.11 kernel and Ubuntu root filesystem with the apps I mentioned above. Stuck my 1TB Western Digital MyBook mirror into the SheevaPlug and I have all the benefits of NAS (low power consumption, small form factor), but without the limitations (what it runs is exactly what I want it to run...), it's also has considerably more horsepower than most NAS boxes too...
If someone is looking for a NAS without the limitations of NAS, then I would definitely recommend one of these.