Surprise! Another question related to Minecraft. Anyways:
Rather than drawing thousands of blocks each frame, I remember reading somewhere that Minecraft breaks the map into 16x16x256 chunks, and every time one of the chunk's blocks is updated, it reconstructs a mesh for that chunk to be used in rendering. The idea is that you'll only ever see a handful of chunks at a time, which equates to only a few meshes being drawn.
This is all fine and well, but XNA doesn't seem to have built in support for creating meshes on the fly. It seems that my only option is to mess around with TriangleLists and the like. Is that the only option, or is there some alternative I'm not seeing?