I have spent about 20 to 30 hours of the past few weeks in order to test the current capabilities of FreeCAD and also in order to learn the basics of FreeCAD. My impressions are that the FreeCAD team has accomplished a few things that only large teams of full time programmers have accomplished in the past. The conclusion I came to after doing my best to familiarize myself with all of the tools that are available in the latest release of Free-CAD is that until FreeCAD releases their planned "assembly module", designing a machine with multiple parts may not currently be a good fit for FreeCAD.
Right now FreeCAD would be my preferred open source program to design an accurate 3d parametric model of a part for printing or machining and for opening step files for some basic inspection. (the measuring tool seems to have limited ability to measure between lines and faces of parts only measuring from point to point) The latest version has even added the ability to make 2d drawings with title blocks and projections of 3d models. The sketching and extruding/cutting tools seem to be very powerful, but without using some fairly complex work-arounds, it's my opinion that it would not be possible to design individual parts based on the geometry of other individual parts in a reasonable amount of time.
I am very interested to see what the FreeCAD development team comes up with in the next few years. I was going to try to model a small assembly to show how freeCAD could help design a functional box whose parts could be exported to a lasercutter; but it became evident that, while possible, it would have required a few work arounds and more time than I currently have at my disposal. --Rob B (talk) 06:58, 19 May 2014 (CEST)-
Ok, first FreeCAD:
As they say themselves, it is still in the early stages of development. I (Conor) have searched for documentation, and apart from the getstarted  there are 2 nice articles from December (so version 0.9, which btw. is in Lucid already). The funny thing is that for some reason, both are in... Polish! I understand you have polish origins, so maybe you speak Polish. Otherwise just google translate. They give you examples and a better idea of what it is right now capable of.  
So I propose the following: you try to reproduce the steps in the articles, so you get a feeling for it. But then regardless stick with Blender a bit longer, and try FreeCAD again when version 0.11 or 0.12 comes out.
Undo doesn't work
Using FreeCAD 0.13.1828 on Windows.
- Situation: I draw a box and modify it's size. Then I hit Ctrl+Z (or Redo from the menu).
- What happens: Box is deleted :-(
- Expected: Box returns to old size.
What is the Assembly module? I presume you are thinking of an assembly module for freeCAD. We (my employer (Vanderbilt/ISIS)) may be situated to provide such a thing.