Can't say that I have used E-Machineshop; however, I have used DraftSight extensively in the past year and have been very impressed with it. I have a very strong background in more conventional programs such as AutoCAD, Inventor, SolidWorks, and also packages such as MasterCAM and SolidCAM so I think I can make some pretty good comparisons about its relative worth. Here is what I would say based on this:
1. The program is free and not just for home use, but commercial use as well. This is not something that a lot of other free CAD packages offer.
2. The program is pretty much a dead ringer for AutoCAD. If you have worked with any AutoCAD program in the last 15 years you will be able to work with Draftsight quite easily.
3. Well it is not a CAM package, you can easily work in dxf format and transfer your files to other cam programs for generating toolpaths, I have done this many times.
4. It is not a 3D software, or a parametric modeling package which means it will never be on the same footing as programs like SolidWorks, Inventor, ProE, etc. This does not take away from the great uses for a truly great 2D drafting program with much of the same capability as AutoCAD. If you want to draw up traditional 2D shop drawings for steam engines and other projects, even for sale, this program will work great for that application.
5. I suppose that SolidWorks (the company that really controls DraftSight) might change the program over time and it might end up charging for it. I doubt it though.