The $300 system, which consists of a pair of identical-looking boxes, one transmitter and one receiver, takes an HDMI signal from a source component, runs it through your home's AC wiring, and spits it out on the other side for your HDTV to display. AR says the system isn't designed to work from room-to-room, like Ethernet-over-powerline adapters, but in our tests we were able to get it to work between rooms.
Unfortunately, our tests also revealed that some video quality was lost in the translation. The signal on the other side was slightly degraded over what we expect from a true HDMI cable (i.e. perfection), showing lower resolution and some subtle choppiness, as if it was dropping frames.
On the other hand, some casual viewers might not notice the difference, especially on smaller screens. And if you're faced with the choice between degraded video and a fat installation bill to string a long HDMI cable run through your walls, you might want to audition the HDP100. Just make sure to get a solid return policy, since performance can vary depending on the state of your household wiring.