Well... External QA for app which costs 2.99$ (or less at times)? No. We just tried to make sure it worked properly - some code reviews, several unit tests to cover some nasty edge cases and that's it. I really hope everybody is alive and well. :)

Also it did help that the users grew confident in it over time. It was not like these overnight success stories (not even success story) which you hear all over the news :)