Also see: Sagnac distortion
“GPS observation processing must also compensate for the Sagnac effect. The GPS time scale is defined in an inertial system but observations are processed in an Earth-centered, Earth-fixed (co-rotating) system, a system in which simultaneity is not uniquely defined. A Lorentz transformation is thus applied to convert from the inertial system to the ECEF system. The resulting signal run time correction has opposite algebraic signs for satellites in the Eastern and Western celestial hemispheres. Ignoring this effect will produce an east-west error on the order of hundreds of nanoseconds, or tens of meters in position.[72]”
http://en.wikipedia.org/wiki/Global_Positioning_System#Relativity
Note: this in addition to the two other relativistic effects in my earlier Wiki post (#80):
http://www.freerepublic.com/focus/chat/2491839/posts?page=80#80
Yep, the fact that simultaneity is relative leads to all kinds of unexpected consequences.
I think all of this is fun :)