How I Use It
We use iMovie to create digital stories, book trailers, and commercials (among other things). The students enjoy creating and showing their work. Most students are motivated by the opportunity to share their learning with this tool and are easily able to learn the interface (many know it from owning Apple devices). I recommend using storyboards and rubrics (or other type of outline) to keep students on track and focused on completing the current assignment. I also recommend requiring a photo/image credit slide at the end to make sure students are properly citing their work.
I believe iMovie is a high quality learning tool. It can be used to explain, demonstrate, narrate or summarize (plus other higher order thinking skills) just about anything. Most students are comfortable with the interface right away (especially those who own Apple devices) and those who are not will catch on quickly. I would recommend that the teacher be at least a "comfortable" user of the program to assist and supervise students in the beginning of the project. My 2 pieces of advice for using iMovie would be 1) be sure to use storyboards and rubrics as it is easy to lose focus and forget the learning goal and 2) students need to be aware of copyright and plagiarism rules at all times.