I would say let's make a list of what CHDK allows, in which situations it helps and update it when needed.
I'm gonna make a list first of what I can remember but feel free to add whatever features I may have left out.
Shooting in RAW
Live histogram (RGB, blended, luminance and for each RGB channel)
Zebra mode (blinking highlights and shadows)
DOF-calculator
Battery indicator
Scripts execution (exposure/focus/... bracketing, intervalometer and more)
File browser
Text reader
Calendar
Some fun tools and games 
Autobooting
All sorts of useful informations on screen about the camera's parameters and clock
Motion detection
Remote cable release for photos and video
Stereo pictures helper
Allows exposures of up to 65 s intead of 15 sec
Switchable noise reduction
Video zoom
Allows the user to set the video compression very accurately from very compressed to DV quality and better
Removed 1 GB video filesize limit
Customizable behaviour thru programming
what it helps a lot in:
lightning photography
fireworks photos
wildlife photography
and there are many other uses for motion detection
timelapse movies
stereo photos
HDR photosI also have a hunch that CHDK will keep impressing us and there are more amazing features to come. Im sure I'll check back sometime in the future to see if I was right
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