Here’s an interesting story about how Verizon eliminated a tiny feature (a checkbox indicating a successfully sent SMS message) and discovered that users apparently relied on that feedback.  This video clip is from AdAge so they don’t discuss the human factors angle but it’s there!  I can’t embed the video so check it out:

NEW YORK (AdAge.com) — A tiny check-mark box on Verizon’s text-messaging screen has taken on new sorts of meaning in the last month. For one thing, its removal sparked a customer outcry.