Shaders modifies the EntityRenderer, Tessellator, RenderBlocks, RenderGlobal, RenderLiving, and RenderEngine classes. Usually, if you install this mod after other mods it will work fine. However, there are a few exceptions.
Incompatible Mods
Optimine
Optimine does not work and will likely never work with Shaders.
Wild Grass
The latest release attempts to detect Wild Grass and install correctly with full functionality but some bugs have been reported. Wild Grass will work if you install it after Shaders. However, doing this will prevent any sort of bump mapping from functioning correctly.
CJBMods
Extreme Increased View Distance
GLSL Completly overwrites the files used by this mod. n.class and px.class.
Optifog
Optifog for 1.5_01 (B Version) does not work with Shaders due to both modifying rendering methods.