Don't collapse unread messages
Messages that are longer than 6 lines only show the first 6 lines followed by a "See more" link. This helps with vertical space, but it's inappropriate for messages that I haven't read yet. When the messages are unread (i.e. below the "new messages" text) they should be fully expanded and the link should read "See less".
Yes, please less automagic!
Scott Wolk commented
At least add a user setting to keep messages expanded by default. Hipchat doesn't contract messages by default and we have webhook connectors for deployment, etc. and we have to expand, ie. "Show more" every time a new message is created. Very annoying for our users.
Allow messages to be marked unread.
If you accidentally scroll down but want to come back to a channel, there's currently no way of saying "I haven't properly read these messages yet".