I did lots of work on exception handling. Most of it now works (fully compatible with J2SE 1.4). Some highlights:

• java.lang.Throwable is remapped to System.Exception (for maximum compability with .NET code)
• Throwable.getMessage(), Throwable.getCause() & Throwable.toString() all work, and are fully compatible with J2SE 1.4. Additionally, the message is stored as the System.Exception.Message property, and when the exception object was constructed with a cause, the System.Exception.InnerException property is set.
• Stack traces now work (fully Java compatible), except for J2SE 1.4 inner exceptions stack trace dumping.
• I made the XML remapping language more powerful. It now supports calling helper methods and using locals to twiddle around with method arguments.

Things that don't work:

• When .NET code prints a stacktrace from an exception thrown by Java code, the stacktrace only shows the stack from the last rethrow point in the Java code.
• Throwable.printStackTrace() doesn't yet support Caused by: in the stack traces.
• Additional exception information object (that contains the stacktrace and the cause)  is not yet garbage collected when the exception goes away.

Here is the testcase I used.

Updated the snapshot.