Most of the "important" features of Direct3D 11 will be exposed immediately as OpenGL extensions.
Well, given the fact that the most important feature of DirectX 11 isn't Direct3D, but in fact is DirectCompute, OpenCL would be a better suited equivalent.
And OpenCL integrates nicely with OpenGL, just like DirectCompute with Direct3D.
But beside a few simulation eye candy like water surface or debris during an explosion, it won't cause much difference in games (because otherwise the physics would influence too much on the game play).
That is, until monstrous power hogs like Crysis 3 and Windows 8 are out. Then the users will have to buy modern hardware en masse, and the install base of DX11 hardware will increase. Only then the developers will be free to safely harness DXCompute for complex physics simulations at game-play level.
Imagine a massive stock car race with Rigs-of-Rods -grade physics simulation of every single vehicle - much more realistic collision and more fun, but would require massive acceleration. If a game developer decides to go for DirectCompute as a possible acceleration solution, better check that most of the user have DX11 capable hardware ! (And be ready to say good-bye to PlayStation & Nintendo players)