I used a coupler to connect two 25' sections (50ft total) from PC to 53" Sony, for DVD playback.
Didn't notice any degradation of signal. Worked fine.
But then I switched to X10 DVD Anywhere, 2.4GHz wireless system (about $50 after coupon).
Even though the X10 uses composite video, it is by far the best long distance solution.
Coupled that with Logitech Cordless Desktop, and you are set.