How is it stable if it is based on an inherently unstable currency? And what about people who don't live in the U.S., A.K.A 17/18ths of the world?
People who don't live in the U.S can still us NuBits, just like people who don't live in Europe, can still use Euro. NuBits just acts as a way to digitally send money to someone using a currency that is pegged to the dollar.
If you have any more questions, you can ask them at the forums, which can be found at: http://discuss.nubits.com