I'm curious: does anyone have any idea what a Powermac that is on or asleep all day is going to cost on the electricity bill? My apartment has all-bills-paid, so I'm not able to do any comparisons, but would you all say this amounts to $5? $10? Surely not more than that... Right since the GX is supposed to offer power savings over the FX, should we expect a drop of $1/month in energy costs? (and no, I'm not *that* cheap, just curious)
While it's sleeping you can probably save more money in the house by putting the power bricks onto strips that you turn off until you need them. All those added up are probably your biggest power leaks in the house, along with VCRs and cable boxes -- general rule of thumb, if it's warm or hot when you aren't using it or have it turned on, it's wasting a crapload of juice. The computer in normal mode -- get rid of halogen lights and use fluorescent lights. Halogen lights may be popular, but many places are getting rid of them to drop the power bills. The computer in full power mode -- now you're chewing some dollars.
If you're letting the machine go to sleep, I'd say it's fine really. Macs, unlike a lot of PCs seem to go into a "suspend to ram" state when sleeping. This means that power is cut to everything but the RAM, so it shouldn't really add anything noticable to your bill.
How much it costs is not that simple. What type of PowerMac? What's in it? (RAM, # disks, and pci cards) What type of display(s)? How many hours a day is the system running versus sleeping? How many hours a day is the screen on versus sleeping? (It can be way different from the system itself)? What USB & firewire devices are you using? Especially ones that draw power from the system. How much does a kilowatt cost where you are? Presuming an average config with an Apple LCD screen running say 10 hours a day and asleep the rest of the time, with electricity costing 20cents/kilowatthour that you are spending at least $25 a month on electricity for it. This is just a [very] rough estimate, but it should answer your question. And the difference betwene the FX and GX could be a dollar a month, but it would depend on some many variables of the system design that just looking at the processor chip(s) is too narrow a focus.
I don't really have any idea, but you can spend $30 to find out for yourself. Check out the Kill A Watt at Amazon.com.