One of the pitfalls of designing a course is that the designer does not consider the user into the plans, or thinks they know better than the user.
I have had trouble in the past with this issue. My circumstance was such that it lended itself to that very attitude. I was teaching very young students (Kindergarten in Korea - age 5-6), and I was teaching students a second language that happens to be my native tongue. It is hard to accept that very young children speaking a second language you grew up speaking have much to offer in the way of helping you design lessons and content. However, much like 'satisfying the cat', I still had to make them learn and happy. I am seeing that more clearly now. The only feedback I generally used was how engaged the students were and their facial expressions. I am now teaching older students and redesigning the class I am teaching, so it has been thrust upon me how important good learner feedback is. Especially now that we are scaling it up to more classes.
I generally use quite a bit of verbal interaction for feedback. I ask the students as much as I can what they thought of certain things. I have done that a lot this year in regards to the online environment I have been trying out. I realize that is not enough though. First, many students are too shy or not interested enough to offer a response. This means I could be missing a large percentage of my students' voices that might disagree with the students who are talking to me. Secondly, I am trusting their honesty when they speak to me directly. Some students will likely exaggerate one way or another based on my presence. They know I am looking and listening to them, and that can alter the feedback for better or worse. And finally, they are put on the spot because I ask them when I have time, not necessarily when they are ready to answer. I have a schedule to follow and meet, so I cannot accept responses on their terms. In other words, even when trying to avoid this pitfall, I am still not getting the whole picture.
This year, I am planning on creating many opportunities for students to offer feedback, so I can get the best possible information. I will still ask, but I will also have surveys and discussion options for students. The surveys offer anonymity and the discussions offer flexibility.
The final pitfall is how to use the feedback. I think some teachers that collect good data might still fall into the cherry-picking pitfall. Getting good feedback from your users does not work well if the only feedback addressed is what fits with what you wanted to fix anyway. This is a common problem for people and data/statistics in the first place. I will try and be as objective about the feedback as possible and accept that there might be things I will not be comfortable with that still need to be done. I am not talking about unacceptable things the students request, but a style of teaching I am not comfortable with or lessons, games, or materials I am not used to using.
I think the best way to avoid these pitfalls is to accept that everything we design to teach with is a river that is temporary. If we can accept that, we just might not hold on to certain aspects of our instruction too hard and we will be able to change with the feedback and times.
I find it funny that I keep coming back to a quote (though unconfirmed) by Coco Chanel, "Get dressed, then take one thing off." She was speaking of women's habits of over-accessorizing, but I feel it can apply to almost anything. Design something, then be prepared to throw some of it out, or change some of it without being too attached. This is the way design will work best.