The Latex plugins really make things interesting. The LaTeXText package [1] allows formula rendering and editing from within the Inkscape canvas.
For tidy circuit diagrams the CircuitSymbols plugin [2] produces exquisite results by hooking into Latex's circuitTikz package and dumping the rendered result on the canvas. Typically I generate a bunch of circuit promitives and then connect them afterwards using snaps and the line tool.