I am having sort of the same problem. Exchange 2003 with BES Express, w/2 users on Curves. When an appointment is created in outlook, it wirelessly synch's to the Blackberry almost instantly. When an appointment is created on the Blackberry, it never reaches Outlook.
This is the first real issue I've ever had with my Blackberries, and it is stumping me. Any help/ideas? Should I look at a particular thread that I didn't find while searching?