The lights. I'm not fond of overhead fluorescent lights. The color and brightness give me headaches after a few hours of computer work. In an office, you have control over the color, brightness and type of light (direct, indirect) but in a cubical setting, you have don't have much control.
Noise never was much of a problem when I was in a cube farm. Speaker phone usage in the cubes was strictly prohibited. Actually, I find it noisier now that everybody has moved to real offices. Sometimes, I swear it sounds like there's a gd carnival out in the hallway :|