Some tips...
1. If you want to mention someone simply put a + or a @ in front of their name. You'll see a dropdown list as soon as you start typing. They will be notified that they are being called out. (red box in upper right of window)
2. putting special characters around your text changes it's properties. -strikethru- _italic_ *bold*
3. You can send private messages by typing one specific recipient's name in the sharing field and deleting everything else.
4. You can stop people from sharing your post with others by going to the post's dropdown and choose "disable reshare" can also disable comments the same way.
5. Hangouts let up to 10 people video chat at the same time. (I've haven't done one yet, but it seems pretty cool.)