If you send another user a private message and request a reply, please make sure you have your PM privacy options set so that your recipient actually can reply to your message and doesn't get a "message cannot be sent because of user privacy settings" notification when they try to send you a reply. The maximum I will do is go to your LJ profile to see if there's an e-mail address listed. If not, well. I'd say sorry, but I'm not!
*disables private messages altogether* I'm reachable via furiosity@lj, and since LJ seems to now require that you get all your notifications in your inbox, I'm always afraid I'll accidentally delete a PM when I'm mass-deleting comment notifications (I get those through e-mail and never use the inbox for them). Though the inbox is a good place to look if you're not getting your comment notifications via e-mail!
Also, Firefox doesn't think "inbox" is a word. Get with the times, Firefox. :|