I hooked my SX100 up my laboratory power supply, and made some measurements regarding the power consumption.
All measurements were done with the screen brightness set to minimal.
Setting the screen brightness to average adds an additional power consumption of 40mA. Setting it to maximum adds
70mA. Disabling the screen by sticking something in the A/V out saves 70 mA (70mA less than minimum brightness)

SX100 Power consumption @ 2.5V

	Without CHDK	With CHDK
Playback mode	190 mA	190 mA
"P", idle	530 mA	~535 mA
"P", half press	670 mA	~675 mA
"P", idle (MF)[sup]1[/sup]	670 mA	680 mA
"P", half press (MF)	670 mA	680 mA
"Video" mode, idle	660 mA	670 mA
Recording video	680-780mA	680-780 mA
Charging flash	810 mA (2 sec)	810 mA (2 sec)
Zebra, hist. idle	-	540-550 mA
Zebra, hist. half press	-	670-690 mA
Auto DR curve processing	-	630 mA
Raw sum/average (Play)[sup]2[/sup]	-	230 mA
Raw sum/average (Rec)	-	570 mA

1) Indeed, enabling manual focus causes the camera to consume 140mA more! Even when i disable the "MF Point zoom" Magnification thing, the additional power consumption stays.

2) Apparently those CPU intensive tasks dont need that mach power after all. 40mA additionally only. Custom Curve processing on the other hand needs 100mA more.

As it seems, running CHDK actually causes a slightly increased power consumption, but obviously not mote than 5-10mA. Unfortunately my power supply isnt that accurate, it only shows steps of ten (0.44 for 440 mA e.g.), so if the power consumption is fluctuating between 530 and 540, i can only guess.. (that when i rounded to ~535 e.g.).

Enabling zebra & histogram needs some a small amount of additional power too.. Then again, those increases are so minimal, it's not worth to worry about.

The manual focus thingy is probably interesting for time lapse photographers.. Running manual focus causes the camera to use around 140 mA more power constantly, using a normal focus method needs up to 960mA with every half press - but only for a short time, around half a second. So, when the camera is set to shoot only every 15 seconds for example, it would need less power to use autofocus...

BTW: The SX100 runs fine with voltages from 2,3V (Batter indicator starts blinking below 2,25V) up to 3,70V.
I didn't want to raise the voltage more, as i'm afraid of frying my camera, but i thought that it might interest someone that the cam runs with a range of voltages.. I guess there's no real need to throw out 50 bucks for a canon power supply..

Edit: I totally forgot about the power saving mode! When my cam goes into this mode, it only needs 140mA. I guess it would be quite nice if we had an ubasic or lua command to activate this mode, so the cam can be sent to sleep when its doing nothing.. (Again, useful for time lapse photography)