The pcb would have to be either tacked with an adhesive, or have a very small bolt or screw through it. The case can and will morph to any needed design, so there is some leeway with everything.
Small, light, strong, comfortable, functional. That's what I'm going for. I am currently focusing all my effort onto the housing and a pcb that was custom would be awesome, I could build it, i just need an eagle file.
The gimmick with the arduino, and all MCU's for that matter, is there simplicity. An arduino is nothing special until you start adding on to it. Making it into a SWRF comm set, or a clock, etc.
The same should apply with this device. If you want to add a screen, go ahead, but one will not be included in the base model. A special shield, however, would be a great idea, the ArduWatch's cap is removable, and a new cap (shield) can be replaced. That was the idea at least.
All of the Femtoduino's pins are being breadboarded out onto the watch itself, so you can develop on-the-fly with just a computer and the device that's always on you. With a bluetooth module on the board, a smartphone could be used. Again, trying to make it as easy to develop sketches on-the-go as possible.
I plan on releasing multiple sizes, with different versions. The final product will include a battery of some sort, there will be a bluetooth version, as well as a USB only version. "Caps" will be released as well for added functionality.