There's a longstanding and mysteriously ignored flaw in OS X File Sharing.
If I connect to one of my Macs using afp, I can browse all the folders belonging to the user I've connected as. I cannot, however, browse the shared folder -- as any user!
I wonder why this only annoys me ...
Update 4/14/07: I thought I knew a fix for this, but I was fooled. If you create an alias to the Shared directory and put it in your home directory, it looks like a remote client can get to it. Wrong, OS X simply redirects to the local shared directory!
I wonder again why I'm the only person who seems to notice this ....
Update 4/15/07: I've been looking at this from a few angles, and this is a real wart. My guess is that the Shared folder is a kind of kludge that was stuck into the OS as a temporizing measure. There's no standard way in OS X (non-server) to create a network share that everyone can access! The one folder available for local shares is not network accessible! (Insert more exclamation marks.) Grrr.
See also: the Parents folder.
Update 9/3/08: This was fixed in 10.5