This is going to sound pretty vague but I'll do the best I can
Last year (or was it the year before - getting old, ahem) I saw a great demo, which I am sure was posted here.
It was a AE-based composting demo, featuring a full screen demo with the voice-over of the artist as the work was being done.
The scene in question featured a live action shot of an urban street, basically a row of store fronts at night, with an actor walking across the street, then up and down in front of the store.
The final sequence looked really simple but as the demo unfolded it showed an incredibly complex set of composites and rotoscoping steps, adding all kinds of signage and light effects to the stores, and manipulating the movements of the actor, so that he was first walking in one direction down the street but was then reversed to walk the other.
Just in case this rings a bell with anyone, as I'd really like to see that again.