Version 4.1.18 has been released and subsequently updated. If you downloaded it prior to 28/8/2010 then please update as there has been a minor fix for stability issues, and some extensions to the Python interface.
4.1.18 features a separate command line entry from the message window area, which makes it possible to use the up/down arrow keys for command history traversal.
Also the python command line interpreter can now handle multiple indentation correctly. The original code used the example in the Python Extending/Embedding FAQ to check code entered and set the prompt according to indentation, however the example code does not handle more than 1 level of indentation correctly – this has been fixed.
Various Python extension functions have been added to return a Python list rather than a dbObjList, and extension functions have been added to get all insts/pins/nets of a cellView.
Lastly the chop command now maintains paths as paths when chopped, rather than converting them to polygons. Alas a side effect of this, due to the implementation, is that undo/redo does not currently work for chopped paths. This will be addressed in future.