It is actually a very cool tool, BUT when you do not simple designs things are not going WELL per see...
I have version 3.0 and have not upgrade to 5.0 yet.... I downloaded the demo and run it on my PC and the same it FREEZE the PC, the same it does on V3....
Apart of that, you can do nice conceptual sketches.... like this one:
And the same I begin on Revit 8.1, and actually the same, you have to wait every time you open your project, and they even show to you a message about it....
I have very up-to-date PC's... so the memory or video or whatever is not an issue....
Regards,
Luis.
Correction: now I am adding just small portions of the whole 3D object.