I just had perhaps the nicest and most useful feedback from a user I have ever received:

In his first email, he asked for a feature, I quickly responded that I've added it to the roadmap and thanked him.

He appreciated the quick response so much, that he proceeded to provide the most detailed and useful list of things I can do to improve my app I have ever received.

Goes to show: Treat your users with respect, and they'll give you back much in return