The working group (HDMI.org) that sets HDMI specifications has not set a maximum cable length. Instead they require that approved HDMI cables meet a required performance standard. At this time it is expected that conventional, reasonably priced copper cables up to approximately 16.5 feet in length can meet the required performance standards. HDMI will usually work with 5 meter (or less) cables, longer ones can just add to the difficulty. Not to say that every problem is due to long cables, however it is evident (and proven) that signal loss is usually the primary culprit and long cable runs are usually where the signal loss is going to be the greatest. The good news is that the cable manufacturers have made tremendous strides in the past couple of years with ratings, testing, equalization equipment, amplifiers, etc. - the bad news is that we are sending more and more data down the HDMI "pipe" and will continue to do so as color depth, resolutions, and bitrates increase.