The current "recommended release" is the port of r31 of the C++ version. This is out of date by Box2D standards (which is at r70+ by now).
Our source code has been updated to r70 along with some XNA specific perf improvements. Please try the latest version out from our "Source Code" section and let us know if you find issues.
We have a few tweaks to make, but we intend to have a new "recommended release" out soon which will include the latest port and additional performance improvements, along with some bug fixes.
Your feedback is welcome!
Our philosophy is to stay as close to the C++ version as possible for easy porting (on our end and on your end) but we really want to have stable and performant physics for Xbox 360.
We also intend to make Box2D.XNA as performant as possible on Windows Phone 7 devices, which will be a natural extension of the XNA platform in the near future.
So, if you guys are seeing any performance issues and can provide us with source code then we really want to take a look at it. We have a set of use cases and performance benchmarks but being able to see how Box2D.XNA is used in real applications
will be invaluable to our performance tuning, especially with respect to our latest Source Code version.
Thanks for trying Box2D.XNA!