The framerate is pretty bad...like across the board. Dark Souls was only bad really in Blight Town. No idea why the performance has taken such a hit.
I noticed this too, it never hits the lows of Dark Souls, but it seems to be constantly struggling in a way Dark Souls never did. That said, I went to Redbox and picked up the 360 version and woah! I'd swear the framerate is almost double what it is on the PS3 at all times. It sucks because I think the souls series works so much better on a Dualshock controller.