|Auto-Mass - Select a material preset to calculate mass|
1) An "auto-mass" feature, which calculates the mass of objects based on their volume sizes (mesh-objects just use the bounding box for now, which may overestimate in cases) and a "material" preset (which provides density information about the type of material that your rigidbodies are made from). Activate this tool from the "Change Mass..." tool in the toolbar, from the RigidBody panel. No more guessing mass values for hundreds of fragments by hand anymore!
2) An experimental patch from Sergej Reich which makes the collisions work properly out of the box (i.e. fixing the various problems with mesh-mesh collisions many were having).
These material presets currently include just a subset of things which I think will be useful for most Blender users. There's the ability to use a custom density by specifying the "custom" entry and then editing the density value afterwards, for fine tuning this yourself.
On reflection, these presets may even be nice to integrate as part of the physics settings instead. However, that is a matter for later, once people have had a chance to have a good play with this.
Now, the next target is getting some sort of caching/baking system in place...