My receiver really did a bad job upscaling 480p via component. If that's what you're doing, you may want to do a comparison between your receiver and a direct connection to your HDTV.
I imagine most receivers are not built with great upscalers.
For now, my setup is a little weird. My projector take 1080p, but output only 720p. There's not component input, but it works with the vga input (using an adaptor). I'll do the test this week. That will be a pain though... I know I have too much connections between consoles and the projector, but man, that's a lot of cable management for 13 consoles plugged at any time and I want to make it easy for my girlfriend. My receiver pass all to HDMI, even old composite cable.
I read somewhere that the component cable for the GC is better than the one for the Wii. (?)
Edit : Well, it's hard to find information on the upscaling quality of my receiver (Denon avr-s900w).