I try to gather feedback in most of my lectures. Sometimes it's very formal, such as post-it notes (thanks Daphne Loads) on a flipchart, sometimes it's tacit/informal, such as observing body language, questions, etc.
I've been surprised that some of my students this term have said, in the feedback notes, that they would prefer not to give feedback at all.
So here is a reason for students to give feedback:
On Tuesday I asked for feedback from my Informatics Entrepreneurship students, and one of them asked why I didn't show the subtitles for the short video clips I use in class. And the simple answer is that I didn't know that the Stanford e-Corner site had that functionality. It's right there on the window interface, but because I'm a native English speaker, and I know the buzzwords and topics, it never occurred to me to look for it.
To be sure, sometimes feedback is more nuanced, and responding would require more sophisticated thought, but this is a brilliant example of how feedback can work simply and beautifully.