I installed Natty yesterday and it gave me the option to install "Experimental 3D support for NVIDIA cards" (which I'm assuming is Nouveau). Now, is there a PPA I will need to add to receive regular updates for the driver or will Canonical push updates out to me automatically?
Unless there are security fixes or certain bug fixes specifically for the drivers in Ubuntu, it is unlikely that you will get regular updates of the Nouveau drivers.
You can read more about Stable Release Updates on the wiki but basically once a version is released it does not change much.
Nouveau is an open source graphics driver so there will be improved drivers each Ubuntu release. Nouveau's 3D support is rather new and there will definitely be performance improvements by the time Ubuntu 11.10 is released.