content access and navigation in Facebook
I noticed that there is disconnect between a content's identifier (URI) and the content's presentation. The correspondence is not one-to-one; the presentation is also affected by how the content was accessed - directly, or from within some page/widget.
For example, while browsing through a photo album, the photo viewer appears as a modal widget. Going to the next photo in the album adds a new entry is the browser's history. Yet, when a history entry is navigated to directly, the photo is not presented in the same manner (non-modal).
I'm a bit torn about this; the purist within me is up-in-arms by the lack of a correspondence. On the other, the URLs are a bit cleaner, since they don't have to "encode" contextual information (how the content was navigated to, the scroll position of that).
This is novel for me. Off the top of my head, it is not trivial to do this in angular.js (my current frontend framework of choice), but it'd an interesting experiment to put this in action (where applicable, of course).