The only GPS system which offers a level of accuratcy which can be compairable to ILS or the Triple Internal Nav system found on most long distance Airliners is Differential GPS. Basically it hooks up the Derated GPS signal (Derated by the gov. as told already), with a ground based transmitter. This allows the aircraft with the right GPS system to get highly accurate nav. fixes. The Idea was to allow aircraft to use this system insted of ILS during landings, but it hasn't seemed to get off the ground. The only people I've heard using this differential system are the U.S. Coast Guard (Basically linking their GPS system with Loran) and Surveying people who use basically the same system.
I reject your reality and subsitute my own