Canon today announced three firmware updates which address recently discovered

acknowledged camera problems.  One of these fixes a camera hang issue which could lead to a loss of buffered images.

For the RebelXT:

This firmware update incorporates the following improvements:

Fixes the phenomenon of extreme underexposure when using some lenses.
Fixes the phenomenon of auto power off function failure when auto power off is set more than 2 minutes.
Fixes the phenomenon of incorrect white balance when using an external flash.

For the 1DmkII:

This firmware update (version 1.2.2) includes the following additional functons and improvements:

When pressing the DISPLAY button immediately after shooting, the LCD monitor would turn completely white, the camera would hang, and the images in the buffer memory would be lost. Countermeasures for this issue have been incorporated into this update.
Errata in the German and Russian language displays have been corrected.

For the 1DsmkII:

This firmware update (version 1.1.2) includes the following additional functions and improvements:

When pressing the DISPLAY button immediately after shooting, the LCD monitor would turn completely white, the camera would hang, and the images in the buffer memory would be lost. Countermeasures for this issue have been incorporated into this update.

Errata in the German and Russian language displays have been corrected.