Where I work, we have fairly extensive, JSON-based web services in all out applications. As a quick example, here's what you would get if you were to GEThttp://config.ssbe.example.com/configurations/90 with the mime-type application/vnd.absperf.sscj1+json:
Our app is very (JSON) web-service heavy, and so having helpful error messages in our web service documents is pretty important. Luckily, Merb makes this, like everything, a metric shitton easier than it is in rails. There are a couple poorly documented things I had to stumble through, so I thought I would write some up on how to do this.
In several of my pages, I have a side-bar menu-y thingie. I didn't want to have to rewrite a controller-specific layout each time, but luckily Merb supports something similar to Rails's content_for block that I wrote about earlier. In Merb, its done using throw_content(API) and catch_content(API).