Also, TIL that it's not a Venn diagram if it doesn't contain all possible intersections, a restriction that doesn't apply to Euler diagrams. So representing an empty intersection by two non-intersecting regions is, technically, not a Venn diagram; and Venn diagrams for more than three sets get harder and harder to draw. Check out the informative Wikipedia entry.
I have a previous entry on humorous Venn (and Euler) diagrams around the Internets.