attaching GP-1 GPS unit to D800

Is this a real problem? As a general rule one tends to use flash indoors, when one usually (if sober) knows where one is without the need for a GPS?

This is applicable to D3s, as well, and it is my experience that anything mounted in the D700 hot-shoe stops the built in flash from operating, but, for me, no problem - a simple choice of either flash or GPS!
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Richard