Comcast DVR's regularly come under fire for bugs, sluggish performance etc with little information available about software updates, known issues etc.  I recently discovered the Motorola DVR/Firmware and Software wiki which reports latest available firmware, changelists, fixed and known issues with each release of hardware, firmware, and software.  A useful resource when communicating your issues with your cable operator.

How to use a Motorola DVR/Firmware and Software - Wikibooks, collection of open-content textbooks