NVIDIA can't directly utilize the Linux kernel's DMA_BUF buffer sharing mechanism -- a zero-copy way to share buffers between different kernel drivers whether it be DRM or other sub-systems -- due to GPL-only kernel symbols and bickering amongst kernel developers.
While their binary blob is off-limits from using DMA_BUF directly, Aaron Plattner came up with "PRIME Helper" to reduce re-implementing DMA_BUF functionality in every driver while also introducing new lower-level hooks for the DRM PRIME import/export functionality.
The patch by Aaron was merged into drm-next last week. This makes it part of the pull request that will go into the Linux 3.9 kernel and could eventually lead NVIDIA to properly playing with PRIME / NVIDIA Optimus support on Linux.
There's also related DMA_BUF improvements that will be coming to the Linux 3.9 kernel.
Other graphics-related work for Linux 3.9 includes KMS locking, the Intel no-reloc performance optimization, AMD Radeon HD 8000 series support for the unreleased hardware, Radeon DRM improvements, work on the open-source Tegra driver, and many other kernel changes.