I've added a couple of additional features to my jsonViewer, Subscriber count and embedded stylesheet.
The green number now shows how many subscribers the observable has, which is good. However, there are a couple of caveats. Firstly, it's important to note, that if a child observable has a subscriber then its parents subscriber count will increment by one. Also if the observable is bound to a DOM object it will increment the subscriber count. Its not just the number of subscribing functions.
Check it out on github or the examples with subscribers.