First time I've ever heard of this: firmware updates for memory cards.
Canon reports that using Lexar CompactFlash memory cards with its DSLR cameras can result in lost images. The solution? Get an update from Lexar, available by the end of May.
The problem? Images can be lost, although Canon says it is "extremely rare." It would be interesting to learn of the technical details that cause the problem.
* Cameras affected are: EOS-1Ds Mark II, EOS-1D Mark II, EOS 20D, EOS Digital Rebel XT / EOS 350D Digital / EOS Kiss Digital N
* Memory card affected is: Lexar Professional 80x-speed Compact Flash card.
But not all lost images can be blamed on Lexar. Canon DSLRs (EOS-1Ds Mark II, EOS-1D Mark II) also lose the image captured in the camera's buffer memory when you do this:
Press the [DISPLAY] button immediately after shooting with the camera set to "RAW+JPEG (high image quality)" causes the LCD monitor to become entirely white and the camera to lock up, losing all the images in the buffer. (This happens with any brand of memory card.) Remove and re-install the battery to restore the camera.
Canon plans to have a firmware fix available by end of May. In the meantime, they say to "make sure the access lamp is off, indicating that files have been written to the media, before pressing the [DISPLAY] button to check captured images.