I put the font name wrongly, and then restarted the idle screen from the command line. I hit the lock button to go to idle, which then failed to start (just flashed black/off very briefly), dropping me back on the terminal.

Then I might still have been able to fix things, but I accidentally went out of the term to another program, then I couldn't come back, the device locked up / crashed, rebooted and went into reboot cycling, from nil to the point where it should briefly show the idle screen (just before asking the SIM pin).
I shut it off by holding the power button for several secs.

Tried to restart without the SIM, no change, same thing.

And I'm certain that that was the only system thing I was touching.
Ah well.

What bugs me more is that it's still on 1.0... no swype, lots of other things still missing.. :-(