I'm a happy Piazza user.
I love using Piazza for answering student questions; the user interface is unbelievably nicer than anything else I've seen. It is easy to enter text and easy to see what questions need answering; It is just easy to use.
Thank you for Piazza! It has been an excellent resource for our new introductory biology courses here at Yale. Piazza is a great forum for those students who are too shy to ask questions in class and who post anonymously - and then this benefits all the students who read the answers. Plus, I have had students say that they love how quickly their questions get answered, instead of waiting for office hours or the next lecture.