Chartier over at Finer Things in Tech reports that it can be used to flip a coin, and to even roll a dice.
As you can see in the screenshot below, tell Siri “Flip a coin,” and “Roll the dice” and it will respond promptly with an answer.
As one user has found out, there are times when Siri’s coin can fall into a crack.
It’s not clear if Apple has added this recently or Siri has been able to do this for a long time. But it’s definitely not an iOS 7 feature as Siri can do this in iOS 6 too.