I'm pretty sure you mean Component as well, not Composite. However, the quality difference is fully dependent on the type of TV you have.

quote shadowj

you sure you're putting it in fully Inu? The only cables that fall out now and then out of my TV are the scart cables from my Freeview box and Xbox. All others are firmly in place

quote smoke N a pancake

However, the quality difference is fully dependent on the type of TV you have.

There is a difference, but (as Red noted a little while back concerning S-Video Cables) some TV's either won't show a difference or will actually show up worse in HDMI than in Component. That seems to be a rarity, however, but I'd still only bother with an HDMI cable if you're using a tv with progressive scan (720/1080p).

Hrm, so at least we installed it properly. We had a 42" with 780p and then a 50" 1080p installed in two different rooms that we used HDMI cables for. The picture was crystal clear, so it turned out alright.

HDMI, like DVI transmits through digital streams. The visuals are transmitted as data packets making the display accurate to the pixel.

As opposed to analog signals(component, s-video, AV, etc) transmits through wavelengths and frequency. Though the picture to a certain degree can still be rendered at high quality, the picture doesn't display to the same accuracy as when displayed through a digital stream.