It can be done relatively cheap by reverse engineering a $15 power meter you get at home depot and combining with $10 worth of electronic parts and a $20 Arduino. Was a college project, and we blew up 5 meters before it worked. Working with 220V (or 110V) right next to 5V can be dangerous and not an easy "electronics problem".

it is my understanding that Wattvision taps the entire electrical system via the meter, not just a single outlet like a $15 "kill-a-watt" style power meter will.

That's true, but you need a combination of the two: both general and appliance-specific measurements. Like the post says: it's hard to figure out where power usage is coming from. If you have more specific data and combine it with simple switching, you can achieve a much better awareness and higher savings. And the hardware doesn't have to be expensive as the "kill-a-watt" devices show.

As a sidenote, are people actually saving money with it? The energy bill for my apartment is around $30/mo. At $9/mo for WattVision service, and $249 for the hardware, I can't find any potential cost savings in there.

My last electric bill was $266 (also in an apartment). I don't think your costs are necessarily typical (and I know mine are not -- mine tend to be high due to medical-related expenses).

Who else can you buy this from?

Www.Theenergydetective.com is another option. I think I paid $135 and found $50/month savings right away.

Curious as to what the 50 per month was from?

The biggest chunk of the $50 was a malfunctioning electric water heater. But we went on to save $160/mo. more. The biggest surprises were 3x 20 watt doorbell inverters, the DVD player that never shut off, the desktop computers, the old TV, and 5-6x 10 watt draws that were hard to track down.

Now our electric bill is 15% what it used to be with no real change in our behavior. ($40/mo.) Actually, we've increased the amount of light in several rooms.