hi su, it does make a difference, especially at low shutter speeds, or long focal lengths.
i've had my 520 for two years now and rarely turn IS off. even in good light and on a monopod, you can see a difference, the only time i do turn it off, is when on a tripod, or panning.
With the 2x crop factor of the sensor, even with the 40-150 kit lens, you need to keep the shutter speed at 1/300 or higher, to avoid camera shake.
Keeping the shutter speed above the focal length can be difficult at times without raising the iso too high (which can introduce noise) so IS is good in more ways than one.