CRTs use less with a black background and more with a white background. That is why some people were trying to get Google to turn their background to black, save energy.
As far as LCDs being much more efficient than CRTs, of course they are. I can't believe some of you are even arguing that. Some of you are stating how much power it consumes by what the power supply is rated at? Come on, that is complete BS! The power that power supply uses depends on it's load. I really thought better of some of you...
As far as turning off computers, it is a good idea. But if you need the super quick boot time, put it to sleep. I have an intel iMac and it uses 3 watts (via Kill-A-Watt) when it is sleeping. This is the same amount of power it uses when it is off, since it is not completely unplugged when it is off (digital on switch). So I just have my computer set to goto sleep after 10 minutes of no use, and if I am going to be gone for the weekend I unplug all of my stuff so it draws no extra current.