One further comment which I don't think has been explicitly made: The people who wrote the modules you use likely did so because they had some use for them and also enjoyed creating something useful. I'm sure it gives them pride and a sense of accomplishment to know others think enough of their work to make use of it. I don't think there is any reason to feel that one needs to "give back" by contributing one's own modules unless you happen to have one to contribute. People contribute in different ways.