Having just purchased a new Widescreen Digital TV I was looking forward to playing my Gamecube on a decent screen. I then noticed that my new TV had component inputs. I'd read that using a component cable gave a superior picture to the standard composite cable supplied with the Gamecube.
I must confess that I thought that the picture on my TV was excellent just using my standard cable and so was a little sceptical about this cable. However, any fears I had were blown away when I changed to the component cable. Everything is so much 'crisper' and clearer, the colours improved, and it really does make a big difference. The clarity is now as good as if I was using a dedicated monitor. It's worth mentioning that this cable is purely for the graphics aspect of the Gamecube. You still need to use the standard phone cable for audio output. Whilst the instructions on the box are all in Japanese, there is also a clear diagram so setup should be straight forward.
If you've got a decent TV that has component inputs, my advice would be to get one of these cables - when you do, it's almost as if you've upgraded the graphics card of the Gamecube!