A way to 'extrude' a path, quickly giving it a pseudo-3D look

Select a path, then select the extrude tool. Click and drag the mouse away from the path, and release. This 'creates' a copy of the path, and joins up the original path's nodes to the copy's matching nodes. The resultant union is added to the document, either to replace or in addition to the original path. It's like extruding in the 3D-box tool, but not bound by vanishing points, and not restricted to boxes (or rectangles) but would work for any path. It might possibly automatically add shading effects. See the wiki page for an image which explains this better.