It works pretty well and I'm generally pretty happy with it, except that the firmware has no method to upload custom characters to the LCD, at least nothing documented on the GitHub page or that I could find by searching here.
So I added it to the firmware myself. I didn't feel like paying GitHub just to put my updated firmware on there, so instead I'm posting it here, in case anybody else wants it.
The updated firmware has two changes:
1)It allows you to send over up to 8 custom 5x8 characters. Send 0xFE to put it in special command mode, then 0x64, then the character you want to upload (0-7), then 8 bytes that make up the character bitmap. After that you can print those characters (Serial.print(0x00, BYTE) or whatever). Since the characters are 5x8, only the 5 least significant bits are displayed.
2)The splash screen has been updated to be more helpful. It still shows the SparkFun message, but only for 1 second, then it shows the baud rate setting from EEPROM (4 = 9600, etc.) for 1 second.
You'll need either an FTDI Basic or an ISP programmer (USBtinyISP, etc.) to update the firmware. The SparkFun product page I linked to above has some info about this. Basically you just connect the FTDI Basic and then set the board to "Arduino Duemilanove or Nano w/ATmega328" in the Arduino IDE.