We're currently sitting in a Microsoft session on DirectX in Metro, where Microsoft is discussing the improvements they've made to DirectX for use with Metro. Every individual DirectX graphics API is getting some kind of improvement, but of course Direct3D is the most captivating.
Direct3D 11.1 will come with Windows 8 (no mention of it being backported to Vista/7, but I'd count on it). The focus on D3D 11.1 has been on performance and efficiency by adding new methods to more efficiently do some common tasks, but there are also a few new features to quickly mention.
Cap bits are back in a way after being removed in D3D 10; the primary purpose of these seems to be to allow Win8 to better handle supporting traditional Intel/NVIDIA/AMD GPUs, and more exotic SoC GPUs by allowing applications to see if the GPU is a tile based deferred renderer, among other things.
Direct3D has better access to Media Foundation (Windows' video playback/encode API). It's now possible to pipe MF output through pixel shaders before display.
WARP, the software rasterizer, has been given a performance boost
Shader tracing has been added for developers to trace shader performance (previously this would require GPU-specific tools)
Stereoscopic 3D support has been added to D3D. We don't have the details of the underpinnings here, but we expect that this will be the vendor-neutral S3D API users have bee clamoring for, without requiring devs to directly interact with quad buffers on a per-vendor basis
Further Reading: MSDN - Direct3D 11.1 Features