I broke down and ordered a Wattvision device a couple of weeks ago. Here is my setup experience.
Box arrives

Unboxing

I followed the setup instructions, but for some (bizarre, unknown) reason my MacBook Pro (June 2010) refused to connect to the Gateway’s (the little deck-of-cards-sized device is called the Gateway) IP 169.254 IP address under any network configuration or any browser. I used another web browser on another computer and finished the setup that way.
I should mention that I emailed Wattvision when I couldn’t connect. I received an email response within minutes telling me to call the support number. I did, and Savraj walked me through some things. He took my word that I really couldn’t connect. After going through everything both of us could think of, he promptly offered to send me a new Gateway at no charge. I agreed, but thought I’d try the configuration with another web browser first, which worked (so I called him back and told him not to worry about the new Gateway). +1 for great support.
Now with it working, here’s how I actually installed it. First I “repurposed” my phone utility box (I use a VOIP phone now):

Inside the utility box was a CAT-5 cable going into my house. This meant a lot to me: I didn’t want to drill any new holes in my exterior wall or fish a phone line through a finished basement ceiling. I grabbed my punchdown tool and wired up an Ethernet jack:


I tucked the cables behind the phone test ports for tidiness:

Here is the entire exterior setup. You can see the Wattvision sensor strapped to the power meter. To the left of the meter you can see the white phone cable, which emerges below and goes into the phone utility box:

Next, I found where the CAT-5 cable comes into the 66-block in my basement. I added another Ethernet jack (all standard Ethernet wiring):

I plugged in a standard phone cable into this jack and to the Wattvision Gateway, the supplied power to the Gateway. The lights flickered for a second then went dark. Gasp! Did I kill the Gateway? No, it does it again when I remove and add power. Hm…
I looked at the ends of the phone cable:

Ah! Phone cabling is straight through. I wired the CAT-5 cable as Ethernet, so that means I need to reverse the wires in the phone cable:

Plug it in and voilà.
