The physics engine has had some changes which should give better reproducibility and precision/quality for physics simulations. Note that the improved reproducibility is only on the same platform - using a different platform can still behave slightly differently.
Improved precision can be activated via python scripting via PhysicsConstraints.setNumTimeSubSteps(x), with higher values of x increasing the accuracy of the simulation. This will be especially useful for those baking simulations to keyframes.
A new feature 'instant replace mesh' was added to the game engine by Jason Richards (Scabootssca) it allows you to substitute a new mesh for a previous mesh on the same frame.
Other improvements have been some bug fixes including cube maps; font textures; a ray sensor fix by Carsten, and a fix for the track to actuator by mal_Cando.
Also for the 2.43 there was a contest for the best 'Rube goldberg' physics demonstration using the bullet physics library. There were some excellent entrys, you can see the results, download the videos, and download the demonstration blends here.
