Some more fact-checkiing from Ken Tindell via Twitter: "A nickel weighs 5g. It would take 2,755 18-wheeler trucks (max legal tare 80,000 lbs) to carry the money."

Consider how much a billion dollars in nickels would weigh: you need 20bn of them, and at 5g each that's 0.005 kg x 20,000,000,000 = 100,000,000 kg = 100,000 tonnes.

There probably aren't that many nickels in circulation anyway. The New York Times noted in 2006 that there were about 20bn nickels in circulation at the time; rising metal prices were encouraging people to melt them for the copper and zinc. Another dose of reason.