The softbody, cloth and particle physics now use a unified system for caching and baking. The first change is that the results of the simulation are automatically cached to disk when the animation is played, so that the next time it runs, it can play again quickly by reading in the results from the disk. Secondly, there is a unified user interface for baking.
As animation is played, each physics system writes each frame to disk, between the simulation start and end frames. These files are stored in folders with prefix blendcache, next to the .blend file. The cache is cleared automatically on changes. Note that for the cache to fill up, one has to start playback before or on the frame that the simulation starts. The cache can be freed per physics system with a button in the panels, or with the Ctrl+B shortcut key to free it for all selected objects.
To keep the results of a simulation, and not have the cache cleared on all changes, the simulation can be baked. Again this can be done per physics system, or with Ctrl+B for all selected objects. If the mesh changes, there is no guarantee anymore that the results are correct, and the user will have to manually free the bake if it is out of date.
For cloth and softbody, it is possible to edit individual frames of the simulation in editmode with the "Bake Editing" option. The simulation can then be rebaked from the current frame to take the changes into account.
For tweaking physics systems, it is useful to work with the timeline Play button enabled. Making changes will then be automatically be reflected in the results. Further, a new option in the Playback menu, "Continue Physics", will continue the simulating physics system regardless of the current frame. This makes it possible to interact with the physics system by moving collisions objects, shaking a softbody object, etc.
An example .blend file and video for cloth that demonstrates the continue physics option.
