This is a sequel to the old threads discussing the CHDK firmware.
The CHDK fw is a hacked firmware for DIGIC II cameras. Currently
supported cams are A610, A620, A630, A640, A710 IS, S2 IS and S3 IS
(see the FAQ for a complete list).
The CHDK fw implements new features like RAW, battery indicator,
live histogram (RGB/luminance), zebra mode (blinking areas of
over-/underexposure), DOF calculator, scripts (intervalometer,
exposure/focus/... bracketing etc.), text reader, file browser,
calendar, games and much more. New features get implemented
frequently, so check the timeline for the latest changes, or the
FAQ for a complete list.
The CHDK firmware does not touch the original firmware of your
camera. It is an additional program which gets loaded into the
memory of the cam. If you have a problem, just turn your cam off or
remove the batteries, and the CHDK fw is gone.

For further information, a guide, download links and FAQ see the
english WIKI:
http://scratchpad.wikia.com/wiki/CHDK

Timeline:
http://tools.assembla.com/chdk/timeline
Dear Vitalyb, GrAnd and all the others: Thank you so much for
creating this wonderful piece of software!
____
Some screenshots:

Main menu
http://images.wikia.com/scratchpad/images/d/d0/Main.jpg
Histogram (Blended) and Zebra overexposure indicator
http://images.wikia.com/scratchpad/images/1/14/Zebra_diagonal.gif
Script menu
http://images.wikia.com/scratchpad/images/3/3b/Script.jpg
_____
Link to the previous thread:
http://forums.dpreview.com/forums/readflat.asp?forum=1010&thread=24662492&page=1