First of all, this is a great addon. However, while I was playing around with user styles I came across a couple of points, some probably part of the restrictions (but without a list I can't tell for sure).

• 'Clear and Reload Chat' doesn't display new messages in current Better Chat tab until "refreshed" (leave tab and switch back)
• Server errors are not printed in Better Chat
• Certain Info messages are not printed in Better Chat ('Trying to resolve hostname', 'Trying to connect to server on', 'Banned', 'Connected to', etc)
• Pokes are not printed in Better Chat
• Info Messages Icon (anything that is printed by server - purely visual)
• Placeholder avatar is overlaid with Broken Image icon (fancybox related? (The requested content cannot be loaded. Please try again later.))
• Emoticon menu doesn't work in Toggled chat (TeamSpeak default) while Better Chat is enabled

Cheers