When Cut Preview was shown as a usability feature, the first comment was to make Extrude previewable. So as the refactor of yesterday had some issues, going to address the extrude's ones, I found really easy to add preview code (with the same color theme). Right now it miss Dimension but it will be addressed in a day or two.
C# compiling note: To include various classes over the project, you can do it by "using" keyword and a namespace. Removing unused "using" in most files of the NaroCAD project reduces fairly significant the compiling time from around 8 seconds to 7 seconds in a 2.13 GHz dual-core machine (that may depend on your CPU speed, disk drive, cache sizes, how your sourcecode is organized, etc.) but in fact an improvement say just this: if you use Visual C# newer than 2005, always do a "Sort and Remove" refactor option as it will save later some of your time.