Congrats to Jamie, who got my quiz basically right, although missing some subtleties on the Windows side. Full answers:
Windows Xbox 360 Zune OcclusionQuery Yes, except for Intel DX9 cards, where IsSupported returns false (exception if you ignore that and try to use it anyway) Yes API does not exist SignedInGamer Works in development builds, but exception on startup if you try to use it with the redist Yes Yes GraphicsDevice.VertexTextures AMD and Intel have full support in their DX10 cards, but none on earlier DX9 parts. NVidia DX9 cards only support Single and Vector4 formats, while their DX10 hardware has oddities with the reported caps Yes API does not exist MediaLibrary.Pictures Collection is always empty Collection is always empty Yes TextureAddressMode.Border Supported by NVidia, Intel, and newer AMD cards, but not by Radeons prior to X1600 (unpredictable results if you try to use it where not available) Yes, but the border color has to be 0 or 1 API does not exist XACT Yes Yes API does not exist SetFrequencyOfInstanceData Available with shader model 3, but not earlier shader models API does not exist API does not exist
Like I said: too many confusing differences!