Some thoughts about learning curve. Recently I stumbled into this video:
and suddenly found something very useful that I did not know -- selecting unconstrained parts of the sketch. Ooops! I never thought that underlined "X degrees" was really a hyperlink! IMHO hyperlinks belong to hypertext in browser and not to hardcore dialog with multiple buttons and other fancy controls. I think changing hyperlink into a button "show unconstrained" would make this feature more obvious.