I've had a chance to play with it a little more since I originally posted the QCAD link. It is a decent little CAD program...I ended up buying a license for both my PC and my Linux machines. It seems like it bogs down faster than AutoCAD, though...not yet suitable for the kind of large project my firm does, but sufficient for ordinary domestic architecture or simpler work (in my opinion). The most annoying aspect of the program, for an AutoCAD user, is that you can't grab individual vertices...you just have to use the Stretch command very selectively. But there is a nice "auto" snap feature that is somewhat like SketchUp's inferences, except that it also wants to snap to the underlying grid...to make it not do so, you have to make the grid some insanely large size.
I'll take a look at those links you posted, RegH. Thanks.