When I encounter a new language or framework, I fall back on a set of problems dear to my heart -- writing a MUD server. With web frameworks, lately, this has been simplified down into "can I write a long-polling message wall with it?" Simple problem, tends to break most simplistic web frameworks simply because requests are often deferred, waiting for an update.
Here it is in Node.JS, using Express, about 50 lines of overcommented code. I'm sure it could be written faster, but probably not as concisely.
Next up, making a kobold walk around a message board.. ;)