First of all, thanks for these tutorials. You've got some great design work in there.
I just wanted to make a short comment on the perspective section of Australia abstract wallpaper tutorial. In that section, after drawing the rectangle that will provide the perspective, and then moving the corners around, you say:
Select the star traced country object and rotate it 90 degrees counter-clockwise. The perspective extension somehow changes the orientation of the object and we want it to come out right.
What's happening is that the perspective extension considers the "first" node of the rectangle to represent the lower-left corner of the bounding box of the object being smooshed. But when you draw a rectangle using the rectangle tool and then convert it to a path, the "first" node is the
upper-left corner of the rectangle. (You can find out which node is the first node by selecting the object with the Node tool and then pressing Tab. The first node gets selected first.) The extension sees that on your guide rectangle you have the first node in the upper-left, so it rotates your smoosh-object so that it's lower-left corner is now the upper-left corner. Then it performs the distortion.
I'm not sure if I worded that clearly. The Inkscape manual has a better explanation, with pictures, in the Perspective section of the Extensions chapter:
http://tavmjong.free.fr/INKSCAPE/MANUAL/html/Extensions-ModifyPath.html#Extensions-Perspective