It's worth mentioning that car GPS navigation explicitly calculates how plausible each GPS reading is, based on a combination of other position signals and basic physics modeling, and discounts anything that sounds too crazy. If it didn't, simple things like tall buildings would be huge problems.
Yes, they're a serious problem. What I'm saying is that they'd be a much bigger problem for GPS-based car navigation if there weren't logic in place to combine the GPS info with accelerometers and gyroscopes.
