Complete no-brainer on whether to support this, IMO, but:
WARNING: When signing the petition note the cunningly-crafted small print:
"Avaaz.org will protect your privacy and keep you posted about this and similar campaigns" (my italics)
Result: their system automatically signs you up to their mailing list, no choice. Doh! What is it with people who think that their Most Urgent Issue / product / fad / message deserves to be mine, as well?