actually one of the worst problems is getting and keeping these devices in sync mechanically. turn by one angular second is enough to move the dot off the reader if it's a kilometer or so away. This way such things like stretching materials (i.e. building walls) with temperature, vibrations (steps), slow sinking of the building foundations, and a lot of other minor movement problems must be taken into account. Or just the devices re-adjusted once a month or so. My friend has worked at a company where they have such a link. Problems all the time.

I've seen a different interesting wireless data interface: Audio :) Some kind of analysing station was emitting quite loud voice signals through a speaker, and they were received through a directional microphone.
The minus was that with good weather and some specific wind directions, the sound was clearly audible several kilometers away, in the suburb area where I was living. Rather odd though not really unpleasant sound, somewhat reminding that from "Close Encounters". Actually, I located the station by following the sound :)