I sometimes like to do time lapse photography and have had to go to a lot of trouble to do this in the past.
For my G2 I reverse engineered the IR remote protocol to trip the camera at set interval.
For the 300D I used a 555 timer circuit and opto-coupler hooked to the cable remote input.
My old time-lapse page is here - http://eddiem.com/timelapse/index.htm
Now with the release of CHDK for my A650is time-lapse becomes almost trivial to do.
Today I took a series of 256 images through the kitchen window using a 15 second interval.
I set the camera to low res (640*480) ran the script, pointed at the sky and went away for an hour while it did its thing.
The camera just ran on NiMH batteries and with the lcd off it only used around %10 of the charge.
The kitchen window has been used before for time lapse testing so similar clips from older cameras can be found at my old web-page.
The frame were converted to mpg using video-mach and the results are in my video gallery.