One thing I have found very off-putting about HU is the fact that finding my own questions and posts is ... how can I say this? ... seriously non-obvious.
I wonder how many questions and posts are not responded to by the original poster because they forgot they had asked the questions or the post in the first place. Or if they remember about it, they can't find it? I don't use the email notification options in any forum I use, anywhere - I really consider such things as spam. I expect to be able to find all my activity simply and easily on the forum itself, but in HU that really doesn't happen. Instead, it is easier to see the activity, questions, and posts that others have done which is very strange. I think the My Activity option should show everything I've done, not just my responses to other people's questions and posts.
I wrote a post about this, and how I discovered how to see my own questions and posts, just in case anyone else has the same problem :
Going back to the OP though - I agree that people should acknowledge responses they get. It is simple courtesy. I like the idea of an acknowledgement button, to say that the OP has read a response they get.