It seems that it's possible for gravatars and screen names to not be displayed properly in chat. Check out the following screenie:
As you can see, the user chatting is Marco. Marco came in first, followed by the user next to him (whose name I can't remember). Marco's screen name and gravatar didn't appear when he posted a chat message.
This is the second time this has happened to me on chat, both times were fixed with a refresh but I thought I'd report it this time.