1. Everybody wears wooden shoes.
Probably at one time in history this was true (or at least the majority wore them), but it definitely isn't true today anymore. People wear normal shoes just like the rest of the world, except for farmers.
2. Everywhere you look you see the traditional windmills.
In the past, there were a lot more windmills then there are nowadays. They were used to make flour, the main ingredient for bread. These days, only few windmills are left, and they are mainly kept working for tourists. However, you can occasionally see new sorts of windmills that produce electricity.
3. Everywhere you look you see tulips.
Sure, tulips are a major export product, but they are not grown on every square inch that is left in the country.
4. Everybody wears traditional clothes.
Almost everybody used to wear them, up to 50 years ago. But especially after World War II and in the 1950s, clothing changed. These days, you can't tell a dutch guy from a swedish guy by looking at his clothes, and only some older men and women (usually that are 60 years or older) only wear them.
5. Everybody is a drug addict.
Just because the government condones the use of so called soft drugs, doesn't mean that everybody uses it. Since we're used to it that you are able to buy weed (in a small amount) without being afraid of getting arrested, it's not so special anymore. Foreigners usually go totally mad when they first see a coffee-shop where you can buy the stuff, and quite a lot of them come to the Netherlands (and especially Amsterdam, since they think you can only buy it there) just for the drugs. Note: drugs are still illegal, but the government only condones the use of soft drugs, like marihuana. Hard drugs, like cocaine and heroine, are still highly illegal, and are not condoned.
6. The story of the boy holding his finger in a dike to prevent a flood.
There is a story about a boy, Hans Brinker, who sticks his finger in a hole in a dike. By doing that, he prevents a flood. Let me wake you up from that dream: it was made up by some American writer. It is impossible to be true. If there is such a small hole in a dyke, then the water pressure would be enormous, so a small boy would never be able to stop the water by putting his finger in the hole.