I'm thinking here from d3d11.1:
*context switch granularity device information query
*SAD instructions for kernels
*mandatory video formats like YUV etc.. like direct3d 11.1 video support for allowing reading this kind of video formats directly from kernels
*point below should indicate that optional direct3d 11.1 interop suport cl_khr_d3d11.1 extension for accessing DXVA textures directly from kernels
and cuda 4.0 ones:
*device info showing if device P2P copies are in place..

and others expanded like broad texture instructions support in kernels like similar to
*access to cubemap textures
*tex2dgrad (use derivatives)
*tex2dlod (mipmap level select)
*tex2dmultisample (access to wanted sample of multisample tex)
*tex2darray (access tex 2d arrays)