The current ebuild nvidia-drivers (x11-drivers/nvidia-drivers-325.08) is not building against 3.6.10.X kernel. I found a patch under http://pastie.org/8123499 which makes it working properly and created an ebuild using this patch on 3.6.10 kernels.
Created attachment 353578 [details]
Ebuils using the patch
This ebuild auto-patches if kernel is >= 3.6.10
Created attachment 353580 [details, diff]
The actual patch fixing nv-i2c.c
(Quoting Doug Goldstein from bug #447566 comment #56)
> It is and has always been Gentoo's policy to support what NVIDIA supports. The current versions of the drivers do not support 3.10. You are more than welcome to use the capabilities of epatch_user (which are present in all the ebuilds) to make the changes yourself but they do not go into the main tree.
*** This bug has been marked as a duplicate of bug 447566 ***