We've tried Yammer, and it's never really taken off. The nice thing about just copying an email to a list is the barrier to entry is so low -- the sender doesn't have to open a new tab, or create any additional content.

Exactly. The idea of copying email from one inbox to another "shared inbox" is painful.

You could give our newly launched application a try. We're working hard to be a twitter for tasks/teams.

http://taskmessenger.com

Yammer sucks, you are better off using free tools, like Bitrix24. If you need PM, I recommend Wrike or Basecamp.

I can see Yammer not quite working right for this scenario. But HipChat came to mind.

I'm interested in this too - doesn't yammer address exactly this problem?