How many private messages (via /msg) can appear in the Chatterbox at one time?
You decide. At the bottom of the Message Inbox is a text field which lets you choose how many private messages you want to see in the Chatterbox at once. Once you receive more than that, a small message will appear after your N-th message suggesting that you go to the Message Inbox page to see the rest of them. You can also archive messages, to let you read them later. Just click the box on the right marked “Archive”, and then hit the “Submit” button. (See also Using the Message Inbox for more info on private messaging.