i never really had that much of an issue, but it does feel as if the sensor triggers far more sensitively now, meaning, it'll turn (and keep) the screen off much earlier and longer now.
the guy at insanelygreatmac suggests that they just cranked up the IR sensor's power by a bit (so much, that you can actually see it light up on camera) to increase the sensitivity.
but as i said, no real issues for me before :/