Common myth: any nuclear explosion causes total destruction for miles in every direction. Because of this, old drills like "duck and cover" were foolishness at best and cold-blooded ways to placate the populace at worse.

Fact: the area of total destruction is fairly small. Most injuries and deaths by most bombs would be caused by flying debris. Duck and cover is a great way to increase people's chances of survival. If you're right at ground zero then you're still screwed, but there are potentially millions of people living at distances where structures would overall survive but taking cover would greatly help their chances of survival. I blame this on pictures of Hiroshima from after the bombing there, where nearly everything is just wiped clean. People don't realize that this is because most of the buildings in the city were practically built out of paper.

Common myth: following a nuclear explosion, the area will be too contaminated to live in for centuries or millennia.

Fact: the really nasty stuff decays in days or weeks. It may not be the healthiest place to be long-term, but months or years after the event, it's not generally going to be a big deal. Witness the distinct lack of widespread contamination and abandonment in modern-day Hiroshima and Nagasaki for example.

Common myth: a full-scale nuclear war would destroy all life on the planet. OK, all complex life. Well, all human life.

Fact: while it would be an event without precedent in both its size and speed, lots of people would still survive. It would pretty thoroughly wreck civilization and easily kill hundreds of millions or even billions of people, but life would, overall, go on. Many countries would escape the devastation and, while their economics would have extreme trouble due to the devastation of global trade, they would not revert to a pre-industrial state or anything like it. Expect a future with technological advances slowed down greatly and dominated by Brazil, sub-Saharan Africa, and possibly Australia, not a future filled with radioactive wastelands and handfuls of survivors waiting for death in underground bunkers.

Common myth: the electromagnetic pulse from a nuclear explosion will wipe out electronics in the region.

Fact: most nuclear explosions don't produce EMP. You only get it when they're set off in the upper atmosphere, as the EMP comes from the interaction of gamma rays with sparse gasses and the Earth's magnetic field. An attacker with the capability would be wise to set such a thing off over the US, but, for example, a terrorist nuke in New Jersey isn't going to wipe the computers on Wall Street.

Common myth: despite all of the above misconceptions, nuclear weapons are still tremendously frightening and we're all extremely lucky that the Cold War never went hot.

Fact: no, this one is definitely right.