I edit for a lot of clients and we always communicate using the Comment feature. It's great!

But there is one tiny thing that seems to come up over and over. It's that the send button is very small and people (myself included) accidentally click slightly off the send button which throws the "Discard Comment" box. I get emails all the time from clients who think the feature is broken and end up emailing instead.

So, my suggestion: make this button bigger and easier to click.