The system did perform its basic task of transmitting audio and video over the power lines I tried. Unfortunately, in every case I witnessed personally, the video quality wasn't as good as with a real HDMI cable connection. Casual viewers may not notice the difference, but videophiles and others who pay close attention may find that the convenience of the HDP100 isn't worth the picture quality tradeoff. I experienced the problems mentioned below in three different locations with two different HDP100 systems, so while it's possible that the wiring in all three locations, and not the HDP100 itself, was at fault, it seems unlikely.
I first tested the system at my apartment in a best-case scenario: plugging both the transmitter and the receiver into the same socket, to minimize the distance the signal must travel. Most installations will have the two plugged into different outlets in the same room, but I just wanted to see how the device performed at its best. These tests were all done in an apartment where powerline Ethernet adapters worked quite well from room to room. I unplugged them during this test.
First I tried out some test patterns and it soon became clear that something was amiss. The PlayStation 3's typically zippy, smooth progress through its own menu system and through the complex animated menus of Digital Video Essentials: HD Basics was comparatively clunky and jerky, and the text didn't look as crisp on my 1080p TV as usual. I confirmed that the connection was in fact truncating the PS3's 1080p output resolution; according to test patterns it looked like about half the normal 1080 lines of vertical resolution were visible. I switched over to 720p and results were better; there was no apparent loss of resolution.
I could forgive the loss in resolution at 1080p since extra resolution is difficult to discern anyway above a certain point, but I can't forgive the choppiness I experienced in moving video. One demonstration sequence from DVE includes some very high-bit-rate animations (above 40Mbps in parts, according to the PS3's display) that choked up the connection. The video would pause briefly, chug forward, and catch again before moving on. Most large-scale movement, such as clouds moving across the sky in time-lapse, again had that characteristic if somewhat subtle chugging, hitching motion, as if frames were being dropped. Pans and camera movement were also susceptible.
I checked out Spider-Man 3 on Blu-ray and experienced the same issues. In the opening sequence, with Spidey swinging above the buildings, the subtle choppiness returned, and when the camera found Parker looking at the billboard, the moving crowd behind him seemed move with that jerky motion. The same thing happened throughout the movie, from the pan over the newsstand to the movement of Parker on his scooter and so on, in just about every scene. Switching to 720p didn't help.
As a picky videophile I would certainly qualify the jerky motion as unwatchable, although some viewers might not mind it as much, especially in scenes with little movement. In fact, I tested this theory by allowing one unsuspecting viewer (my wife) to watch an entire movie via the system, and she didn't notice the choppiness at all.
I attempted other outlets around the house and the results were much the same. On one in the same room I couldn't get a connection at all, and on the other two in the room I experienced the same kind of performance described above. On the plus side, I was able to get the same performance outside the room, too. I tried two other plugs, one in the living room about 20 feet away, and another in the kitchen about 30 feet away.
After a conversation with Acoustic Research, their engineers suggested my home's wiring must be the problem. I sent the system home to the apartments of two other CNET staffers and, sure enough, both reported no problems. But when I connected the system again at the CNET office--granted, not the best test since power supplies at offices can be worse transmitters of signals--I saw the same choppiness and truncated 1080p resolution. Both staffers said that what they saw at home was better than what we all saw at the office, although one admitted that he might not have noticed the choppiness as much since he used a smaller TV.
Flummoxed, I took the system to my in-laws' house over Thanksgiving weekend to give it a try there. Making a similar connection I noticed similar results. The choppiness in Spider-Man was there, along with more obvious false contouring, as if the system was truncating bandwidth as well as dropping frames. Once I pointed out the issues to my father-in-law, he saw them easily enough, although at first he didn't notice.