hey fallen,
ideally there is the "components and circuit library" for it
http://www.arduino.cc/playground/Main/ComponentLib
this is where I thought you would put the hardware building blocks,
how to interface them with Arduino
from the multiplexers to bluetooth and stuff...
the fact is that components, hardware and software are so much linked together
that it's not easy to know where to put the information
in the Arduino tutorials section for example there are 2 tutorials on connecting
Arduino+bluetooth and another Arduino+zigbee...
the circuit library isn't very popular yet...well the whole wiki isn't very used yet 
(guys start typing please!! 
)
so if you think it would be better to have a interfacing-hardware section I could post it up
what do you think?
is components+circuits library enough? or is better to have an Interfacing-hardware section?
your opinion (as well everybody else) is precious for us all
cheers
b.