... and maybe the real Yun too.
So there's the Arduino Yun. That's quite a nice concept - an embedded Linux computer (MIPS based, YAY!) and microcontroller combined on one board. Just such a shame it's an Atmel microcontroller and not a PIC32.
I don't know about you, but I have a huge pile of different Arduino-like boards here. (I have so many because I need to test UECIDE with them - or that's what I tell the "bank manager"). Many is the time I will have more than one of them plugged in to my computer. Often times I have programmed one of them with some code only to find it's not worked - and why hasn't it worked? Because I have had the wrong serial port selected in the IDE.
The Arduino (and many other boards) have a very useful time-and-cost saving feature ideal for when you are working with buttons and switches - namely internal pull-up resistors on the GPIO pins which can be enabled / disabled at will in software. This means you don't have to clutter your board up with pull-up resistors of your own for all the buttons and things, and also means they can be turned off and on to give your design much more flexibility.
But nowhere can you find out actually what the resistance of these resistors are. Why not? Simply because nobody knows.