Sharing an SD card or USB stick across the network
Why won't OSX allow me to share a USB drive or SD card across my network? I can plug it into my Mac, go to System Preferences > Sharing, and add the card/stick/whatever as a Shared Folder, but the ' + - ' buttons allowing me to assign users to it are ghosted. Therefore it appears on my local network but it's inaccessible.
It's not the end of the world but it's not what I expected from "the world's most advanced desktop operating system". In fact it's something a PC could do at least three generations of Windows ago.
Am I missing something really obvious?
Thanks
iMac (27-inch Mid 2011), OS X Mountain Lion