You can still use your finger. It's just precision that goes down. E.g. if you try to draw with the stylus..

Well have fun..trying.

On the plus side, they really do work. It's just that I don't think they were made for touchscreens in mind, the commercial itself says that they were developed for the military. It would be good for the body of the n900, not the touchscreen itself. Hence why I'm not going with InvisibleShield again.