While the 280.04 beta driver marks the introduction of a new series, the official change-log is shockingly small. All that's officially mentioned for being fixed-up in the 280.04 beta is incremental bug-fixes and preliminary support for the X.Org X Server ABI 11. This is the video ABI that's being used by X.Org Server 1.11 RC1. It's good to see NVIDIA still at the top of their game in supporting new kernel and X.Org releases, while AMD continues to lag behind with their Catalyst driver. It will still be several months before AMD Catalyst is expected to support X.Org Server 1.11.
Download links for the NVIDIA 280.04 beta driver can be found in this forum thread. Hopefully another beta will be out soon where they officially announce other new features for the 280.xx series beyond "incremental bug fixes", as they should have some good things coming down the pipe.