Breaking the Nouveau interface for the kernel DRM is causing the X.Org Server to stop working with this driver and forces the user to upgrade their non-kernel Nouveau drivers. While the Nouveau driver just entered the Linux 2.6.33 kernel unexpectedly at the request of Linus Torvalds himself, he is now outraged over this interface breaking. The Nouveau driver is in the kernel's staging area as the developers knew the API was likely not finalized, but because breaking this interface is huge and causes other problems on the system for NVIDIA users, Linus wants them to have a stable API even when it's living in the staging area.
Linus has talked about reverting the commit that causes the interface break to calling to the Nouveau developers to address the fundamental problems causing this break to taking other measures. Over the past day this has turned into a very heated discussion on the kernel mailing list and is certainly an interesting read. At this point, the commit causing the interface break has not been reverted in the Linux 2.6.34 code-base.