Surprised to see it on the Prius, but then again, I can imagine that as having a substantial blind spot, as cars go. The Dodge Magnum strikes me as another good candidate.
Vans and up are where you find the real market for such cameras. Our shuttle buses at work have backup cameras with a 'V' of range dots printed on the monitor with a Sharpie. The drivers really do refer to it when they can't avoid backing up, and also to keep an eye on the bicycle rack. A backup camera also seems to be an increasingly common RV accessory -- doubtless a factory offering on the nicer ones.
When a full-sized van came into my life, I got one of those "van eyes" lenses and figured out how to incorporate it into my scan when backing up. Even though it's a conversion with lots of large windows, backing up in crowded areas where pedestrians may lurk, such as in a supermarket parking lot, always makes me feel like the Sorcerer's Apprentice. A camera, especially one with some low-light capabilities, is an intriguing prospect now that the prices of cameras and small LCD displays seem to be coming down.