Perhaps this is really mean or unfair, but to use your words, "We're surprised you didn't catch that."

Some opinions on the app:

1) Signup is annoying, but at least you let me use it right away without clicking on some verification link that is now in my inbox

2) Something about the login/signup form design says this app is not very good or perfectly sculpted. Maybe it's the padding between the text fields or how little space you use of the giant browser window there is. Take a look at Google's or the modal form on AirBnb. There's space, sensible padding and layout.

3) When I first log into the app and see "Double Click Me" and I double click it, the right-slide-in modal is fine, but it blocks out rest of the UI. What I would prefer to do (and would expect it to do) is just slide in without dimming rest of the interface. That right-pane should remain in place when I click on another item. It should repopulate with that item's details. Dimming and drawing attention to the right-pane is fine for the "Learn to use NubiDo" but for everything else, it feels pedantic

4) Is there a better name than NubiDo? This comment feels shallow, but I am not sure anyone would take an app with the name "NubiDo" seriously. Sounds like (and maybe it is) "Newbie Do" which doesn't sit right in the mouth and just sounds funny. There's gotta be a better noun or a verb you can use. Even Any.do, Evernote, OmniFocus, or Wunderlist is better. Even better are simple and grounded names like Things. Yes, a good domain is probably hard to find these days, but I think you need a better name than NubiDo. You can get creative with .ly or .io domain extensions and pre/suffix like "get" or "app" in your domain names...

Not a bad effort by any stretch. Just not up to snuff to be converting users from their faithful and already-established gtd tools.