I know they look good on your desk but it is more expensive than your ordinary box. Does it really save that much electricity?

I'm assuming you're talking about LCD, not Plasma. Plasma screens are large-format TV's (42" + ) where LCD is monitors and TVs from 1"-42+". Flat-panel monitors (as far as I know) are all LCD.

They do save power. It probably shouldn't be a selling point for residential use since it will probably take years for an LCDs power saving to pay for itself (although since CRTs are actually more expensive these days due to demand and shipping costs, it doesn't really matter) it makes a difference for companies running hundreds of screens.

I looked up some 17" monitors with CRTs running 75 watts and LCDs between 25 and 40 (on the 10 models I compared). This is a little skewed as CRTs and LCDs measure power consumption differently, CRT measures "peak" consumption and LCDs measure "Typical" consumption, but you certainly get the point.