http://www.hdmi.org/installers/longcablelengths.aspx Running Long Cable Lengths
Like all HDMI-enabled components, cables must be tested to meet the Compliance Test Standards set by the HDMI Licensing Administrator, Inc. Cables must successfully pass a signal of a certain strength (Standard cable must deliver a signal of 17Mhz; High Speed must deliver a signal of 340Mhz) to pass compliance.
The HDMI specification does not dictate cable length requirements. Different cables can successfully send HDMI signals various distances, depending on the quality of the design and construction. As well, HDMI compliance testing assumes “worst case” scenarios – testing with components who have minimally performing HDMI electronics. That is why you may see cables in the market that claim to successfully pass an HDMI signal at very long lengths. This may be true using certain quality CE components on each end, but may not work in every case. It is best to test entire systems before installing
http://www.hdmi.org/learningcenter/faq.aspx#44 FAQ: Does HDMI accommodate long cable lengths?
Q: Does HDMI accommodate long cable lengths?
Yes. HDMI technology has been designed to use standard copper cable construction at long lengths. In order to allow cable manufacturers to improve their products through the use of new technologies, HDMI specifies the required performance of a cable but does not specify a maximum cable length. We have seen cables pass "Standard Cable" HDMI compliance testing at lengths of up to a maximum of 10 meters without the use of a repeater. It is not only the cable that factors into how long a cable can successfully carry an HDMI signal, the receiver chip inside the TV or projector also plays a major factor. Receiver chips that include a feature called "cable equalization" are able to compensate for weaker signals thereby extending the potential length of any cable that is used with that device.
With any long run of an HDMI cable, quality manufactured cables can play a significant role in successfully running HDMI over such longer distances.