1.0

Dynamic plugins.
Physics: explicit joint damping based on joint velocity. Joint friction and efficiency not supported.
Dynamic spawn and removal of simple objects from the world.
Basic sensor simulation (e.g. range, force and image sensors).
Option to run in headless mode with image sensor simulation disabled.
Supports urdf model loading.
ODE physics engine.

Future changes (1.1+)

Tool for removing complex robot objects such as PR2 dynamically from worlds.
Sequencing object spawning (e.g. create table before putting the cup on it). This is achieved by naming a dependent object when spawning. The spawner waits for existence of the dependent object before the model is spawned.
assimp based mesh loader (with Collada support).
Supports ODE and Bullet physics engines.
Supports GPU shaders: per-vertex lighting, per-pixel lighting, normal and tangent maps (this depends on whether Ogre 1.7 makes it into visualization_commons).
ROS-ified gazebo node that offers services for interacting with simulation. Deprecating any environment variable requirements when starting gazebo.
Improved GUI for object manipulation.