Ah, poop. The COG LCD I soldered to the board was lighting up whenever I applied power - so I assumed it was working and that a little code-fu would let me make the magical characters appear on it... no such luck. I tried and tried, I hooked up the Saleae Logic analyzer to it and verified I was putting out the correct stuff... but still nothing.

A bit of investigation caused me to do this:

I found that I had correctly made the footprint for the backlight... but the rest of the pins were backwards. That got me frustrated, so I tried to remove it but the result was just a mess and I gave up and started cutting it off.

After cooling down I soldered the circuitry for a regular HD44780 style LCD to the board. Then the LCD itself. It tested fine after powerup. There you have it - always triple check your footprints.