Block (1.8)

isNormalCube(blockaccess, pos): forge, delegates to opaque material, full cube, and not providing power. Determines redstone properties, pushing out of blocks, etc.. Replaces the below, though should override both in case

isNormalCube(): delegates to solid material, full cube, and not providing power. Appears to be the main logic method. Used in grass spreading, finding spawnpoints, etc.

isOpaqueCube(): used for 1.8's aggressive chunk culling

isFullCube(): appears to be used for rendering (fence connections, model quad baking) and a few other miscellaneous things (/clone command, enderman placing, AI)

isBlockNormalCube(): delegates to solid material and full cube, appears to be used for ambient occlusion and some visual connections (vines, redstone)

isVisuallyOpaque(): used when rendering first person (suffocation) overlay