At certain angles strong infrared sources such as sunlight or incandescent lights will cause the system to fail to track properly. We have a test system located in a room that has one outside window and only incandescent lighting. It works fine except when placed at certain angles to the light.
Fluorescent lights are never a problem.
Accuracy varies from user to user. An absolute pointing accuracy of about one degree over a 30 degree range can typically be achieved. An adjustable smoothing function takes the median gaze point from several frames and moves the cursor to this combined position. This allows the user to tradeoff response time for smoother cursor movement. Glasses are usually not a problem.