"This is the key -- how much precision does your application really need ? I doubt that many need more precise than 1 ms."
Light travels at about 1 foot per nanosecond/1 meter per 3.34 ns, so if you wish to compute your location to the nearest foot/meter, that's how accurate your time needs to be.
Traditional GPS gives you your location to within 10m at a resolution of 40ns but I believe gains a little from multiple sources. 1ms gives you your location to the nearest 250 meters if my math is correct (probably not...)