Good post Laurian — Putting query language into a search box is pretty terrible. It’s even worse when it’s already there and you can’t get rid of it.
Still, don’t some of the problems you’re talking about still exist in the form based approach? While this might cut down on certain user errors like mismatched parenthesis or putting an operator in the wrong spot (do you have numbers that show improvement btw?) — the problem of building a useful query is not necessarily solved in the form. How does the form help with the too narrow or too broad problem?
This was a timely article for me — thanks for posting it!