It's difficult to tell from the videos as to what the PS3 is capable of, but the graphics from the trailers come in two categories. Either they are so good that I can't tell wither they are in-game or pre-rendered as in the case with Assassin's Creed or they look exactly like an XBox game running on a 360 with poor graphics, but a nice sharp resolution as in Bladestorm.
If you watch the Bladestorm trailer you will realise that it is short and poorly encoded. This is the state of most of the PS3 trailer so far and I believe this is deliberate on Sony's part.
Would link to a few more, but I have an IT Service test at twelve and I want to get there early.