@ghowriter 

Go to sharing content and security located in the Advanced > USB Sharing menu. You should see the folder directory that has been detected so you can pick and choose which folders you want to share.

@Tony @ghowriter 
I second need for better control over media server, and suggesting just turning off sharing some directories is NOT a solution.
I have backups and saved games - which have pictures and sound files I do not care to see on my media server, yet I need to share them.
Let me choose what directories (from the shared ones) the media server access - other routers like Linksys lets me do this.

@Tony @ghowriter 
This is actually a security risk.
I may share files and directories with a password, but by design media server does not have a password - if I cannot limit which of shared file server directories it use, it will share pictures I may not wish to share!