I'm on an Exchange Server with a ton of folders and server-side rules that automatically move the incoming messages to folders. I've been looking for the same solution for years. Unfortunately,
AFAIK, there isn't one.
I upgraded to 6.5. At least with that version, Outlook is much more finger friendly, so you can quickly expand your folders and see the new mail counts. Unfortunately, you won't see the "folder" number counts on the summary calendar icon.