My HDTV dont have HDMI so I use the compontent cable as my TV cant support 1080p, only 1080i as far as it can go.
Most PS3 games support 720p and cant really go higher. Very few PS3 games that actually support 1080i/1080p such as Metal Gear Solid 4.
For blu-ray movies, it is recommended to use HDMI for that since blu-ray movies are better in 1080p than 720p. If you view blu-ray movies in 720p, it wouldnt really be that much of a difference from DVD movies. with 1080p in blu-ray movies you can really experience the difference.
So HDMI or component dont really matter for the PS3 since it can still be viewed in high definition between 720p and 1080p (1080p is still "not quite there yet" so 1080i is more common.)
Anyway, good luck with the PS3.