Amazingly, out of the 3,858 visitors (according to Google Analytics today) 2,034 URLs were submitted and tested on the app. Clearly a lot of people just clicked the example submission but out of those 1,634 were unique. Granted, some people submitted more than one URL but I think a large majority of people came up with a URL of their own to try. Isn't that amazing! What a turnout of a Friday afternoon hack (with some Sunday night hacking to make it into a decent looking website).
The lesson to learn here is that the Hacker News crowd is excellent for getting engagement. Yes, there are a lot of blather and almost repetitive submissions but by and large it's a very engaging community. Suck on that those who make fun of HN!
HTMLTree has been moved to https://htmltree.herokuapp.com/