Canon today has posted a firmware update for the EOS 20D that is designed to correct two conditions that would cause the camera to freeze up periodically.
The Read Me for firmware version 1.0.4, released today, indicates that instances of the shutter button becoming inoperative during continuous shooting, or when changing lenses while the camera has gone into an Auto Power Off slumber, have been fixed.
Unspecified problems with certain CompactFlash cards have also been addressed.
Firmware v1.0.4 is a free update from Canon's Bebit web site in Japan.
Update, October 5, 2004: The update has been pulled from Canon's web site, and has been replaced by a brief statement: "Firmware update service is not available temporarily." There have been a number of posts on Internet forums indicating that the firmware update rendered the 20D inoperable, so it seems likely that v1.0.4 has been removed while Canon investigates a possible problem.
Update, October 7. 2004: Firmware v1.0.5 is now available for download. Details of the changes are in this article.