System Information
Linux Ubuntu 14.04 32bit
NVidia GeForce G102M

Blender Version
Broken: 2.73a

Short description of error
the scale/sizes of import/export for STL mesh files are multiplied/divided by 1000

Exact steps for others to reproduce the error
Based on a (as simple as possible) attached .blend file with minimum amount of steps

Export:

1. open Blender, in right panel set Properties, Scene, Units, Metrics. The default cube is 2x2x2 m, see Dimensions in N right palette, or 3D View: Measure Panel in add-ons
2. File, Export, Stl, Export STL
3. Open FreeCAD, menù View, Environment, Part
4. menù Modify, Preferences, General icon, Unit tab, set Standard (mm/kg/s/degree)
5. Preferences, View icon, 3D view, 3D Navigation, set Blender style (mouse rotate, translate and zoom)
6. menù File, New, menù File, Import, STL file
7. use Measure tool to measure the object, it is about 2 mm

Using CURA a SW for 3D printers http://software.ultimaker.com/
I got the same result:

1. menù File, Load model file, the cube is 2x2x2 mm (the floor checkerboard is fixed to 10x10 mm)

Import:

1. Open FreeCAD, menù View, Environment, Part
2. menù Modify, Preferences, General icon, Unit tab, set Standard (mm/kg/s/degree)
3. Preferences, View icon, 3D view, 3D Navigation, set Blender style (mouse rotate, translate and zoom)
4. menù File, New
5. menù Part, Primitives, Prism
6. select the object (double click), in left panel Properties, Box, set 100x100x100 mm
7. use Measure tool to measure the object, it is about 100 mm
8. menù File, Export, select Mesh Format, name as .stl file
9. In Blender, menù File, Import, Stl, Import STL
10. measure the object with 3D View: Measure Panel add-ons it is 100 m sized

Opening the STL file in CURA, it is 100x100x100 mm

So Blender export STL reduce the size of objects 1000 times, and import STL increase the size 1000 times