I do wonder about the real value of sticking an e-signature to the end of an e-petition, they aren't very verifiable afterall. However, quite a few of the petitions on Change.org have seemed worthwhile and they certainly make it easy to have your voice heard. Looking at this video, perhaps it has made a difference in a few instances. Better than nothing,  but is it better than making yourself heard on the street or contacting your MP? Not sure, check out their results here though.