I found this insanely helpful! At first I thought the tutorial was just a scripted app which only listened for the right queries to move on. I was a little blown away when I realized I could run other queries against the tutorial db.
once you get to lesson 10 or about, it limits the input quite a bit since the lessons start to build atop each other. Before that, or after you are done, you can do a lot.
The commands are executed against a real unicorns mongodb collection (each user having his or her own)...so you are only limited by what's been implemented in the javascript shell and on the thin proxy backend.
This does mean that someone who wanted to take the server down probably wouldn't have to try very hard.