UPDATE: The D3D11 backend basically just as well working as the other video backends these days; the information below is just kept for reference
Okay, so this thread is for everything related to the new DX11 Dolphin plugin. Read the FAQ first please, before answering ANYTHING to this thread, thanks.
Q1a: DX11 plugin? What happened to DX10?
Q1b: Why DX11?? Now I need to buy yet another new GPU!
A: DX11 supports so called "feature" levels which make it possible to use the DX11 runtime even with DX10 GPUs. That means: You're fine with a DX10 card as well. DX9 users are out of luck though
Q2: How does this plugin compare to the existing gfx plugins, speedwise and in compatibility?
A: Performance is slower than DX9 and (depending on your system config) OpenGL right now (in some cases maybe faster than OpenGL). There's still room for optimization, but I can't estiminate how much, yet. Right now, expect about 40%-85% of DX9's speed. (Update: The major bottleneck is very hard or even impossible to fix, requires changes to the common video plugin library)
Compatibility is almost as good as DX9 with EFB to texture and virtual XFBs. With this, most games should be perfect with DX11 and should be playable!
Q3: What do we need DX11 for anyway?
A: There's numerous things to mention here: The new plugin is (in my opinion) a lot cleaner now because of the cleaner API itself as well as because of being rewritten. Apart from that, DX11 provides support for specifying the maximum LOD of a texture and for some vertex element formats (both of these things are unsupported in DX9). Also, DX11 is a bit nicer when it comes to certain other little things. This should allow for higher compability and accuracy than DX9.
However, DX11 will NOT fix logic blending, even though many think so. DX11 only supports logic ops within shaders, but not for blending. That means: The blue box in Mario Kart Wii won't get fixed in DX11.
Q4: What can I do to help here?
A: Implement anti-alialiasing, real XFBs, EFB copying to RAM, hi-res texture support, ...
Q5: omg I just tried the game XXX and it...!!!
Check if it works with other plugins and make sure that the game doesn't depend on any of the unimplemented features. If you're sure you didn't do anything wrong, report it in this thread or even open an issue in our Google Code project.
Q6: Where is antialiasing / texture dumping / hires texture support / feature XX?
Not implemented. You're free to do so
Q7: Did you program the WHOLE plugin by yourself?!
A: Yes, although it started as being a port of the DX9 plugin which was not created by me. Now it has been heavily modified, but there are still many things which the the two plugins have in common (see Q7).
Special thanks go to rodolfoosvaldobogado. He was almost always around when I had a question about anything concerning the gfx plugins and without him at least two major bugs would still not have been fixed
Q8: Why not put DX9 and DX11 in one plugin?
A: That'd be the longer term goal. Anyway, keep in mind that DX9 and DX11 are quite different APIs. Not as different as DX9 and OpenGL, but anyway it's still not as simple as just updating the 9 in all function calls to an 11
tl;dr: This plugin is PRETTY stable, but not guarranted to be in your specific use case. However, it's in a fairly good shape and if DX9 doesn't work for you, DX11 might be a good alternative to OpenGL.
Okay, so this thread is for everything related to the new DX11 Dolphin plugin. Read the FAQ first please, before answering ANYTHING to this thread, thanks.
Q1a: DX11 plugin? What happened to DX10?
Q1b: Why DX11?? Now I need to buy yet another new GPU!
A: DX11 supports so called "feature" levels which make it possible to use the DX11 runtime even with DX10 GPUs. That means: You're fine with a DX10 card as well. DX9 users are out of luck though

Q2: How does this plugin compare to the existing gfx plugins, speedwise and in compatibility?
A: Performance is slower than DX9 and (depending on your system config) OpenGL right now (in some cases maybe faster than OpenGL). There's still room for optimization, but I can't estiminate how much, yet. Right now, expect about 40%-85% of DX9's speed. (Update: The major bottleneck is very hard or even impossible to fix, requires changes to the common video plugin library)
Compatibility is almost as good as DX9 with EFB to texture and virtual XFBs. With this, most games should be perfect with DX11 and should be playable!
Q3: What do we need DX11 for anyway?
A: There's numerous things to mention here: The new plugin is (in my opinion) a lot cleaner now because of the cleaner API itself as well as because of being rewritten. Apart from that, DX11 provides support for specifying the maximum LOD of a texture and for some vertex element formats (both of these things are unsupported in DX9). Also, DX11 is a bit nicer when it comes to certain other little things. This should allow for higher compability and accuracy than DX9.
However, DX11 will NOT fix logic blending, even though many think so. DX11 only supports logic ops within shaders, but not for blending. That means: The blue box in Mario Kart Wii won't get fixed in DX11.
Q4: What can I do to help here?
A: Implement anti-alialiasing, real XFBs, EFB copying to RAM, hi-res texture support, ...

Q5: omg I just tried the game XXX and it...!!!
Check if it works with other plugins and make sure that the game doesn't depend on any of the unimplemented features. If you're sure you didn't do anything wrong, report it in this thread or even open an issue in our Google Code project.
Q6: Where is antialiasing / texture dumping / hires texture support / feature XX?
Not implemented. You're free to do so

Q7: Did you program the WHOLE plugin by yourself?!
A: Yes, although it started as being a port of the DX9 plugin which was not created by me. Now it has been heavily modified, but there are still many things which the the two plugins have in common (see Q7).
Special thanks go to rodolfoosvaldobogado. He was almost always around when I had a question about anything concerning the gfx plugins and without him at least two major bugs would still not have been fixed

Q8: Why not put DX9 and DX11 in one plugin?
A: That'd be the longer term goal. Anyway, keep in mind that DX9 and DX11 are quite different APIs. Not as different as DX9 and OpenGL, but anyway it's still not as simple as just updating the 9 in all function calls to an 11

tl;dr: This plugin is PRETTY stable, but not guarranted to be in your specific use case. However, it's in a fairly good shape and if DX9 doesn't work for you, DX11 might be a good alternative to OpenGL.