If you love using Ubuntu, but love to use Unity 2D for whatever reason, I have some bad news. As shown in the title above, "Ubuntu 2D" also known as Unity 2D, has been removed from the 12.10 repos. Existing users of Unity 2D in the current builds in 12.10 will be automatically switched to the Unity 3D interface.
This provides a major problem to some users, because some users (such as your's truly) have hardware problems preventing the use of Unity 3D. There is a safety net, though. Those lacking sufficient graphic grunt will get a hardware accelerated interface powered by the OpenGL rasterizer LLVMpipe, whilst anyone with a capable graphics card will see that utilised.
LLVMpipe uses software (CPU) rendering instead of using the graphics card. So if your machine does not have a good processor to start off (like me), then Unity 3D might struggle for you. If you are one of those people, I just personally recommend you stay on 12.04 until any potential issues are sorted out.
Then again, that's my opinion. We'll have to wait and see how this version of Unity works.