I just wanted to thank the community and developers for a great experience w/ bullet.
I created a C# wrapper for and integrated bullet into our engine in 5 working days. 1 day for most of the wrapper (used SWIG w/ a few simple issues), 1 day for testing the wrapper (recreated the c++ examples w/ the c# wrapper), and 3 days for direct integration. Currently I have rigid bodies w/ most shapes and a few constraints.
Feedback wise I would say:
-Issue 477 (closed because its bad timing) - I highly suspect you could wrap bullet cleanly w/ java as well as c# and provide it w/ the repo. I have only wrapped the portions I use, but that is already a good bit of the baseline.
-MotionState was perfect for my needs, but confused me at first when I tried to move bodies when I wasn't calling simulationStep (I added a pause/play/stop to allow our editor to change the initial members of the rigid-bodies/constraints).
-documentation for several components hard to find while I was working to figure some of the basics out. for example DISABLE_DEACTIVATION, sleeping, ...
-You can't change the shape params like size, radius, height, ... without creating a new shape, disposing the old and assigning the new shape to the rigidbody. This might be the core design, but i wanted to point it out.
-source control uses SVN. I think Git would be better; eh.
-API portal doesn't link back to the main bullet site? (not obvious)
Over all I felt like this should have been much harder which is a testament to the bullet project itself imho.
Id also be happy to provide details on how to wrap bullet into C# (Java wouldn't be much different) using VS 2008. SWIG did most of the work for sure and has been a useful tool for a handful of projects.