I used to think I was pretty good at geography. So I thought this Mercator Puzzle, where you just have to move 15 country outlines (out of place, but not rotated) to the actual country locations on the map would be pretty easy. It's not. (Via FlowingData.)
The problem is that this map (like most maps) uses the Mercator Projection to represent a 3-D surface on a 2-D plane. This translation from globe to page distorts country outlines, especially near the equator. That's why most people think Australia is smaller in landmass than the USA, when in fact it's about the same size as the lower 48. (Australia's the easy one to spot in this puzzle -- drag it over the USA to check and see.) When I was at school in Australia we'd often see equal-area Peters Projection maps on the wall (sometimes even with South at the top), but that projection isn't without its own issues.
Enjoy the weekend!