There's a video on you tube somewhere of a tandem where riders face each other. Highly efficient because the stoker's rear aspect acts a fairing for the captain (if you see what i mean)
If that's the one I remember from some years back, it won a few TT's until they managed to change the rules and ban it.
I remember seeing some one using a Janus recumbent tandem at a BHPC meet, and the stoker was taking photographs of the other cycles on the velodrome's banking, as they overtook them. With that sort of bicycle, the stoker is much better positioned for taking photographs of the front of people, rather than the back which is often the case when you take photos from a bike. I always seem to take lots of photos of my back, the sky, and the road, when trying to take a photo of someone behind me!