Having just upgraded to a new TV, we are now connecting most of our equipment via HDMI/component where available. We have a Joytech 540C Xbox Control Centre which ties all our non-HDMI sources together, and it generally works well, switching composite, s-video, component, stereo RCA and optical SPDIF. It also has a builtin 5 port 10/100 ethernet switch (I wish it was gigabit though). Unfortunately, when feeding a component signal from the Wii, the colours appear washed out, and the screen occasionally loses sync.
If you have this problem, the easiet solution (if you have 2 weeks or so), is to contact Joytech, or their Australian distributor - Take 2 Interactive, and request the Wii adapter to fix the above problem. The adapter is a small RCA male -> female adapter, that fits between the green connector of the Wii component cable, and the Joytech unit.
If you like getting your hands dirty, or don't want to wait for such a long time, I received mine today, and I will share with you the secret of its operation. Its a 75 Ohm resistor. Nothing more. All you need to do is connect it between ground and the signal line of the cable. You can either make an adapter yourself (the safe way), hack it into the cable (you'll need another RCA connector - the resistor is small enough to fit inside the connector), or modify your Joytech unit (if you feel like dedicating an input to the Wii, and voiding your warranty).