While the scout reports are perhaps more accurate than having no info at all, in my experience the reports that come from having High Dominion in an uncontrolled province seem to be the most accurate though they don't seem to detect Magic Sites.
I'm not sure about the exact percentages, but some nations have "Spy" units and I can confirm that "Spy" units definately seem to give more accurate reports than "Scout" units.
Originally posted by mlepinski: I'm not sure about the exact percentages, but some nations have "Spy" units and I can confirm that "Spy" units definately seem to give more accurate reports than "Scout" units.