When this support arrives, NVIDIA customers will then be able to additionally use the xrandr utility to configure the display or the numerous open-source graphical utilities for configuring the display such as those in GNOME or KDE.
We don't know when NVIDIA will officially introduce this feature in their Linux driver (and likely Solaris and FreeBSD too), but they classify it as a top priority feature.
Back in August, AMD had introduced RandR 1.2 support for their proprietary driver. Most of the open-source drivers (with xf86-video-nv being one of the exceptions) now support the capabilities found in version 1.2 of the X Resize and Rotate extension. RandR 1.3 is also on the heels of being introduced within X Server 1.6.