On the page Petitioning websites we keep track of all petitioning websites we come across. We compare and adopt best practices in our site.
But a signatory with us can not unsubscribe to the answer a petition gets. If you do not want an e-mail with the answer you need to undo your signature by explaining this to the helpdesk (firstname.lastname@example.org), much like the unsubscribe e-mail to email@example.com, or not sign to begin with.
The difference with Avaaz is that you do not regularly get answers to petitions in those updates. You get indications on the impact a petition had in the number of signatures or attention from the mass media. Perhaps there is a hand over to authorities of the petition, but a formal reaction to the petition is rarely mentioned.
How public your personal data are
Passing on the e-mail address to others is comparable. With the difference that Avaaz suggests that it is possible for authorities to contact you by e-mail if you give permission. With us it always goes through us and never individually: the answer from an authority goes to all signatories.
Also, you can give Avaaz the permission to pass your e-mail address to others as part of a campaign. In the past this was an option with us, but it was hardly used. Now petitioners can ask to subscribe to some newsletter or contact them personally. From there on it is between the signatory and the petitioner, we are not in between.