I'm working on a shapefile viewer for Android, and the file I'm using to test shows the surface land management for the state of Arizona. I zoomed all the way in on the north-west corner of the state and saw this. (The dotted gray line is Google's state line; the green line is mine.)
It looks like my math is off, or the shapefile is wrong, but then I zoomed in on the north-east corner of the state and saw this:
Google's state lines miss the Four Corners Monument by quite a bit, while mine are almost dead on. (I also checked in satellite mode; again, my state lines are almost perfectly on the Monument.) This led me to read the whole backstory of the Four Corners Monument being in the "wrong" place. But the final Supreme Court ruling was that the original survey markers are the legal border, not the description of where the borders were supposed to be.
Has Google drawn its state lines incorrectly? Perhaps they used the nominal borders instead of the survey markers?