I put the board together a couple of weeks ago, but have been unable to get it to work properly. I successfully installed the Arduino bootloader on the ATMega, but can't load sketches onto it. From what I can tell it's because the the reset pin is not being held at 5V (for reasons I don't understand). This is confusing as the master Arduino uses the reset pin of the slave Arduino to upload the bootloader.
The FTDI chip also doesn't work. It's hard to debug as I didn't create any test points on the board. It doesn't show up in the /dev directory, and using the FTDI utility doesn't lead me anywhere.
I'm going to leave this board as is for now and keep the failures in mind for the next revision. I will be using QFPs instead of QFNs in case bad solder connections were the cause of the failures (I have re-soldered both chips multiple times, each time inspecting with a microscope). I will also be adding test points to the FTDI chip to help with debugging.
Below are pictures of the soldered board (yes, those are bodge wires). At least it was fun to put together!