It really depends because some are a LOT more reflective than others.
I bought a LG 15.4" 1440x900 glossy laptop screen and you'd have to be in very bright place and be displaying a dark colour to get much reflection.
However... I bought another one (I don't know what make unfortunately) but it was also 15.4" 1440x900 glossy and no matter what colour was on the screen it was like looking into a mirror, I couldn't work on it at all and had to return it.