I assume there are no visible alerts when you receive a PM from someone, either? And the only way a user finds out about new PMs is when he clicks on My Messages tab or gets a notification in email?
You can activate a popup, aswell as email notifications ->
https://bitcointalk.org/index.php?action=profile;sa=pmprefs There's also always a little [X] mark with the number of new, unread PMs besides the
my messages button, as long as you got some.