The retrieved information is now displayed on the attached LCD.
Issues regarding the unexplained freezes seem to be solved by not using SPI and I²C at the same time. Since the Arduino combined with the Ethernet Shield, still has enough free pins to connect the LCD, I haven't dug into this issue and just control the LCD with parallel connections.
Details on connecting the LCD can be found on the Arduino website - LiquidCrystal Tutorial.
I'm using pins 8, 7, 6, 5, 4, 3 and 2. These pins are configured in lcd_control.cpp.
To read two buttons, I'm using my own DebounceButton library, which you'll have to download to use the latest CdpSniffino too.
One button is used to scroll through the retrieved fields, and the other to scroll through the data in the field (when it's too long to display on the LCD).
As always, suggestions are welcome, but I currently don't have much time to implement new features.
I'm very interested to hear if you're using this tool and what you're using it for. So, if you are, please leave a comment.