As it turns out, Cataclysm incorporates experimental support for DirectX 11, and rather than adding anything visually, it's designed to help speed up performance, too.
Of course, if you want to take advantage of DirectX 11, you'll need a DX11-capable card from AMD's Radeon HD 5000/6000 lineup or Nvidia's GeForce GTx 400 series. You can't enable DX11 through a graphical option. Rather, you'll need to add '-d3d11' to your World of Warcraft shortcut. Or, open your config.wtf file (located in ...\World of Warcraft\WTF\) and add the line SET gxApi "d3d11".