playing the 360 version right now (2 hours in, could be more).
in the first hour, the framerate can get pretty bad. the game pushes a lot of impressive stuff and it takes its toll on the framerate. if you unlock the framerate, you get excessive tearing but it runs a lot smoother. saw the first 30 minutes of the ps3 version and it seems to be mostly the same, maybe more tearing.
after the first hour, framerate gets much more stable and seems to hold the 30 fps target most of the time (while still looking mighty fine).
during combat, it still can get a bit choppy (like in bioshock 1+2)-
framerate aside, the game looks fantastic and IS fantastic. i love everything about it so far, i hope they can keep the pace up.