http://en.wikipedia.org/wiki/HDMI_CEC#CEC
The way I understand it, it is supposed to enable things like turning off other devices when one is turned off.

My receiver is a Pioneer VSX-1120-K and my TV is a Vizio XVT553SV. Can I set up my receiver (or its remote?) to turn off the TV when I turn off the receiver?

I don't want to use one of those triggered power strips because all my devices do things (like update over the Internet) in sleep mode.

The answer is: it depends.

For devices from the same manufacturer and the same model year. It works pretty well.

As those two factors diverge, so does the compatibility. Even if the design specs say that shouldn't be the case.

For power on/off, your chances of it working are pretty good. But still the only way to know is to check the manuals of the components to find out how to enable CEC, and the what options it supports. Then try it.