There is an interesting post on the ozymandias.com blog that looks at the merits of 1080p or "True HD" gaming as Sony calls it.

The really interesting statistic that popped for me is how much less time a game console has to render a 1920x1080 scene versus a 1280x720 scene. (Remember this is on the same console, whichever one you like. This is not a comparison of different console's rendering capabilities to each other.) Simply put, for a 1080i/p game the console has 55% less time per pixel to render any special effects, anti-aliasing, illumination, etc. than for a 720p game. Yes, even Resistance has fallen off the bandwagon and admitted they can't hit 1080i/p as previously claimed. (It also helps explain why Gran Turismo HD is so underwhelming.)