I am noticing that a lot of errors are cropping up in my directX application because I am setting values (depth/stencil state, raster state, etc.) when doing rendering operations and then forgetting to unset those values. In d3d9, it appears that issues similar to this could be managed using state blocks. I'm wonder: what is the best way to implement the same functionality in d3d11? Are there any existing implementations in use that people find to work well?

I wrap up every API in a stateless abstraction. e.g. at the lowest level, every renderable object is made up of (or dynamically creates per frame) DrawItems similar to below.

The renderer then just knows how to consume these DrawItems, which fully define the underlying API state, so it's impossible to accidentally forget to unset some previous state.

enum DrawType { Linear, Indexed, Indirect; }
struct Resources { vertex/instance/texture/cbuffer pointers };
struct DrawItem { u8 raster; u8 depthStencil; u8 blend; u8 primitive; u8 drawType; u16 shader; u16 inputLayout; Resources* bind; u32 vertexCount; u32 vbOffset; u32 ibOffset; };
typedef vector<DrawItem*> DrawList;

In practice, at the beginning of the draw call processing, the default set of states is copied onto a local set of states. The state as available by DrawItem is then written "piecewise" onto the local set. Then the local set is compared with the state set that represents the current GPU state, and any difference cause a call to the render context as well as adapting the latter set accordingly.

I actually do this kind of "layering" earlier, and the result is a "compiled" DrawItem structure
Often I have multiple state vectors being overlaid, such as defaults on the bottom, shaders-specific defaults on top of that, then material states, then per-object states, then per-pass overrides.