I saw the other day that there's a build of the CHDK replacement firmware for the Canon SD1000. (Look for the IXUS70 model, which is the same camera.) I've had CHDK for my Canon S3 IS for a while. It enables some interesting things like shooting in RAW mode, but I actually haven't found RAW that useful on the S3. But now that I carry my SD1000 almost everywhere I go, it's great to have the same firmware for it.
For me the coolest thing it gives you is the ability to script your photo taking. You can have a script do bracketing on most of the variables. The script I like the most is interval shooting. I can easily shoot 90 photos at 1 minute intervals, capturing something like a sunset. It goes way beyond the time lapse video setting on the SD1000. Or I can have it automatically shoot kids at church at about a shot every other second.
There are even scripts (that I haven't tried) that do things like shooting when the scene changes, essentially doing motion detection.