PC Games Hardware reports Blizzard has included an experimental DirectX 11 mode in the latest beta version of WoW: Cataclysm. The new effects don't seem that spectacular though, and the DX11 mode still seems a bit buggy as in some cases the image quality worsens:
If you participate in the beta of World of Warcraft - Cataclysm and if have a DirectX 11-compliant system, you may experience the benefits of DX11 using a modified shortcut.
To do this, expand a shortcut to the woW.exe with "-d3d11". Alternatively, open the "Config.wtf" in " World of Warcraft Beta WTF" and add the line SET gxApi "d3d11" (with quotes). With the experimental DirectX 11 path the visuals changes: Spells now reflect in the water or lava, so do the characters and the sky. However the pretty transitions between water and shore disappear - hopefully, this is just a bug.