Time will tell. I think PS3 will end up having a considerable advantage over 360 graphically. BR-ROM is slow, but there's a hard drive you can use as a cache.
People were in the dark for months in the case of PS3's capabilities, with the Xbox 360 as an established system and a lot of vague comments telling that it was graphically superior or equal. I wondered if it was true.
So I took a DVD-R full of 720p trailers from both the Xbox 360 and PlayStation 3 and meticulously looked at how their performed on my HDTV.
The resulting perception was that PlayStation 3 games look better, if a bit austere texture and color-wise. They had that CGI-ish look to them, and were generally better animated than what I saw on Xbox 360 efforts, and had better lighting, whereas Xbox 360 titles failed to wow me in the same manner to instead recall me of the best performing PC games... of course that might slightly have to do with the fact that many PC developpers love the Xbox 360, but holistically I really do find this observation to be truthful.
And this is with a complex CPU architecture like CELL that isn't fully mastered yet, so over time as developpers will get to understand it and use it to its fullest potential, it's only rational to imagine that the graphics will be boosted.
Make no mistake, these are two roughly equivalent systems that can fully rivalize with one another, however there's no mistake in my view that the PS3 has the edge.
