The good: realistic, specific community of social change folks. Why I have serious concerns: The 1800 people on netsquared are key social change folks in one narrow community. To access change.org they need to go over to that website to become a "captive users." Social change is about new ways of doing things, not creating another site designed to create "captive users." Find ways to link the nodes in the network, not create new nodes with large memberships.
The good: critical technology problem faced by a large swath of the NPO sector (mailing list/online community integration). The bad: expensive problem to solve, no clear partnership/community model for getting that solution used beyond Dgroups.