I have a plate wired to my Pi. https://www.adafruit.com/products/1109 < this one, except mine is the 1107 model without RGB and with only 16 pins. I would show you on fritzing but I can't get it to work properly, plus that part isn't included in the Adafruit Fritzing library yet. Oh well. Essentially I have the 3.3v, 5v, two GND, SDA and SLC pins wired up the corresponding pins on the plate's header.
Reading button presses from code works fine, the contrast pot works fine as well, I've turned it all the way in each direction, no real difference except for the pixel blocks disappear when you turn it up too high. Still no actual text. Turning on and off the backlight from code also works fine. For reference, I'm currently testing with the Adafruit Char LCD python lib, which I found at this github repo https://github.com/adafruit/Adafruit_Python_CharLCD with the char_lcd_plate.py example file.
So as I've said, most of the features work fine, except for arguably the most important one: actually displaying text. It just displays two lines of blocks, no matter what code I send to it.
Honestly, it might be my shoddy soldering that melted something on the PCB that shouldn't be melted and I just don't see it.