The new player has two Virtual Machines, one which can play old content and one specifically for new Flash 9 AS3 based content.
According to an Adobe spokesman the new virtual machine is significantly faster, supports full runtime error reporting, and industry-standard debugging. It also includes binary socket support, allowing developers to extend the player to work with any binary protocol.
Flash Player 9 will also become Adobe's default version. You can find the download here. µ