All that complaining I was making about the parlous state of 3d rendering packages is still true; however, I have discovered that there is at least one exception to the rule.
Google Sketchup is actually surprisingly userfriendly, makes generally good guesses as to what direction you're trying to move in (as 2d projections are always ambiguous), and has a whole set of almost-intuitive behaviours regarding tools (there's a simple extrude tool as a basic option, the tape measure doubles as a guide-line maker and a scaling tool, and all tools colour-code themselves as a cue to the location they think you're in - a corner, edge, midpoint or face).
It is a beautiful beautiful thing. A pity it appears to be Windows only (I wonder how well it works in Wine...).
