I just received notice from my state Society of Land Surveyors. The National Society of Professional Surveyors Governor has drafted a letter to Senator Jim Webb about this issue.
Average GPS users could see some degradation of signal and every cell phone using the proposed network could potentially act as a GPS jammer in close proximity to ANY GPS receiver. Due to the proximity of frequency to the L1 transmission from the satellites, most, if not all mapping and survey-grade receivers could be succeptable to lock interruption (i.e. lose position).
Surveyors aren't the only ones affected by this. Anyone using the GPS signal for mapping, agriculture, LE dispatch, fleet monitoring or other medium precision application could be affected.
I'm not sure that this LightSquared network is the best way to get everyone on the internet from mobile devices.