I imagine a lot of boring scenes occur when the writer tries to cram in exposition in an unimaginative fashion.

Sean, exposition is certainly one contributing factor to "boring scenes". That is, if the exposition is handled poorly. Exposition in and of itself is not by definition boring. If you find something interesting for a character to say, then think about how to deliver that exposition in an interesting fashion, then problem solved. Case in point, the U.S.S. Indianapolis monologue in JAWS. But far too often, scripts feature talking head scenes, one after the other with little or no thought given to cinematic storytelling. Finally, perfect opportunity to reprise that observation attributed to David Mamet: "Never be boring."