Sorry, I should have been more clear with my axis labelling =P
Coming from an OpenGL background, Y is the up/down axis and Z is the fore/aft axis.
Essentially, this is a moot point seeing sensors can be oriented in any way you see fit so as long as I have a clear indication as to which axis is which in relation to the device. For now, I'll stick with the axis convention I feel comfortable with 
I'm wondering how complex this could all get in terms of the math behind it all but I do have a fairly solid Vector, Matrix and Quaternion library I could port into C assuming it will all fit on the Seeeduino =D