Canon has a second update for the software that runs the Powershot S1 is (firmware.) The v126.96.36.199 update improves the "communication processing with CF cards." Not clear what that means. Perhaps the camera now works better with slower cards?
The update is available at Canon Japan's Web page.
The instructions are not very clear. Here's how I installed the update:
1. Download the .zip file from the Canon Web site. (You'll need your camera's serial number.)
2. Unzip into a folder, such as \Canon\PowerShotS1IS_f-2
3. Double-click the UploadFirmware.exe program, and follow its instructions.
4. After clicking Finish, follow the instructions displayed by the readme.txt file.
5. Wait for the update to complete (takes a minute or three).
After doing the update, I found that it reset some my custom settings, unfortunately. I had re-turn off all the sound effects :<
Over on the Digital Photography Review forum, lion1308 found that the firmware update changes "the autofocus behaviour. It seems the camera doesnt keep loosing focus as it used to." Others are also noticing better focusing, including one fellow who did tests with two S1s, one with and one without the firmware update.
As for Canon's mysterious note "communication processing with CF cards", Dutch in SF found this Canon FAQ: "In extremely rare cases, the following problems could occur with this camera, but these have been fixed. If these issues have occurred with your camera/CF card, please reformat the card after updating the camera’s firmware.
* Incorrect information about the capacity of the CF card or the number of images it could store was displayed.
* Messages indicating that the card was malfunctioning or that there were no images on it were displayed, and it became impossible to take new images or play back the recorded images.
* Images that had already been recorded would be overwritten with newly taken images.
* Images taken with the camera could not be played back."