An e-peititon is going to do nothing. This nonsense distracts people from actual effort and helps bills like this get passed.
If you want to make an impact, the minimum you should do is write a letter to your MP, on paper, sign it and send it to them by post. Letters and phone calls (but particularly letters) are the currency your MP uses to gauge public opinion. Use them.
I think the whole point of the government petition website is to gauge public opinion. I think it'll do more than 'nothing'. I'd agree though, write letters as well.
Since an e-petition site like the one linked gives people opposed to an issue the impression that they've accomplished something, those people are that much less likely to do something substantive to resolve the issue they're concerned about [Citation_Needed -- I couldn't be bothered to find it].
So, less is actually done to oppose the issue than if the site never existed in the first place. It actually helps those who are in favour of the issue opposed.
E-petitions aren't useless: They're worse than useless.
If you want to make an impact, the minimum you should do is write a letter to your MP, on paper, sign it and send it to them by post. Letters and phone calls (but particularly letters) are the currency your MP uses to gauge public opinion. Use them.