Hi Stefan,

Part of it depends on what your "Unit Options" in MoI are set to.
I set mine to Centimeters, because I find that most CAD models are built with those units.

In Blender, I also set the units to "Metric"

The other thing to consider is the file format that you export to from MoI.
If it is .STL then when you import into Blender, you will need to re-scale the size.
.OBJ's have the same issue
Same thing for a .3DS format.
Scaling can be found in the "Numeric Panel", use the "N" key while your mouse is over the 3D window.
Don't forget to reset the scaling. Use Ctrl+A, to "Apply" the scale back to the model, once you're done.

If on the other hand you export from MoI as a .LWO you will find that you will not have to re-scale the model.

Hope this helps.

Scott