Heard an interesting tidbit recently...apparently the Sacajawea dollar coins are the exact same dimensions as the old Susan B. Anthony dollars. Of course, the new coins have smooth edges rather than reeded. (the dimensions in question: 8.1 grams in weight, 2 mm thick, and 26.5 mm in diameter...diameter is the only one required in the specification, so I'm not as sure on the thickness and weight equivalence)
That would sure explain how the vending companies did not have to retool their machines for the new currency...and here I thought they had some sort of inside skinny.
Furthermore, I heard that during the approval process for the Susan B. Anthony dollar, the idea of making it gold colored was quickly tabled. Oops. What a difference color makes for near-quarter-sized coins, huh?