[bentcorner]

We use Yammer where I work and some groups use them and some don't. I find that there's very little reason to use it.

Most communication happens in Outlook/Exchange mailing lists.

I do think that Yammer and it's ilk offer somethings that plain email don't - better attachment integration and history (with email you can't see discussions that occurred before you joined).

One thing I don't like about Yammer (and other social networks for work) is that discussions are very "flat". Contrasted to email discussions at my work, which can get very lengthy and include many branches. They wouldn't scale to Yammer at all.