We found that Facebook Groups felt more like a group wall than a product for sharing and collaboration. You can't send attachments via email, and you can't reply with anything besides plain text.

Posterous Groups makes email the core of the product. You can do everything via email including creating a group and replying with rich media attachments. There aren't any restrictions on what you can post.

Facebook Groups doesn't work well as a mobile experience. It's important for me to be able to post and consume content from my iphone. This works well in email and using the Posterous iPhone app.

While Facebook does have a large user base, there will always be people who aren't on the service or don't sign in to it regularly. We're firm believers that email is the best way to reach people.

We've made it seamless to get non Posterous users to understand how a group works and how they should participate. Give it a shot and please send feedback our way.

Thanks!