Thanks! Just received my Yun from Adafruit and had great fun setting up the WiFi and loading my first sketches. What a great way to make Arduino control and programming available over the Web and through a WiFi hotspot!
I asked about the following over at Adafruit Forum--they said they didn't know and the question might be asked here:
Say, what's that 'mystery component' on the front of the board, at the upper right corner of the MIPS shield? Looks kind of like a micro switch with the button missing--shown on the Arduino layouts and images on your (Adafruit) site and Arduino.cc, but not openly identified. Could it be something like an external antenna connector for the WiFi, or is that just wishful speculation?