regarding warranty, you might consider reading this post:
CHDK in the media (it is also in the wiki somewhere).
and yes, you are both right, chdk does not make permanent changes (other than increasing the shoot count by huge numbers
).
by the way how do you know that the camera only was used for 500 shots?
did you check via the vers.req method? this can sometimes lead to surprises, see this thread for example:
questions regarding s3isconcerning the dust @ lens: never heard of that particular problem, i heard more of the "e18 error", which occurs when for example sand or dust is sucked into the lenses' motor and the lens is stuck (the gears are stuck), so in theory the picture quality would be ok if only the lens would extend. see this thread for example:
Canon & E18 Erroroh, by the way, it really is just a coincidence that all the linked threads were created by me