HDMI is great technology, but they're not the most reliable if you have to run the cable over long distances. Ethernet is better with distances, and it's also cheaper. The solution? Use an ethernet cable to extend your HDMI connections, and all you need is this little adaptor.
As Apartment Therapy points out, the cost of running HDMI over long distances is quite a bit more expensive than it is with ethernet. Seems like a pretty good deal.