Having run some forums with chat, may I suggest that you configure FlashChat to show the last X number of messages when a user logs in. This will allow the newly-logged-in user to see that others have gone in there and consider hanging in there for someone. It is also nice when there is an active conversation going for new folks to figure out what people are chatting about. This has just been my experience.
Edit your /inc/config.php
'backtimeOnLogin' => 20,