This wasn't set correctly on geeklair.net (it was at some time, but I probably forgot to reset it when I recovered the machine).
On Mac OS X client, the only supported way to do this is via the GUI (since the Mac OS X Server CLI application one would use for this, systemsetup, isn't part of Mac OS X Client), which would be a problem for me since I don't have (and don't really want) remote GUI access set up for that machine.
Fortunately, the ARD stuff that comes with Mac OS X client now brings along a version (or two) of systemsetup.
Running: `cd /System/Library/CoreServices/RemoteManagement/ARDAgent.app/ && cd Contents/Support/ && ./systemsetup-panther -setrestartpowerfailure on`
Seemed to work. (systemsetup and system_profiler now both report that the machine will automatically restart on power loss).
