Mint and Ubuntu have removed the old way of sharing through nautilus ( Classic Samba ) and replaced it with something called nautilus-share ( Simple Sharing ). You have in fact created a share but it's defined in /var/lib/samba/usershares
not in /etc/samba/smb.conf.
If your interested in this new way I have written a howto on it's use: viewtopic.php?f=42&t=23169
"Classic Samba" is still possible but you need to download the package: system-config-sambaEDIT:
I should have noted that the package system-config-samba doesn't add an option in nautilus. Instead it's a stand alone utility that appears in Menu > Administration > Samba. Also of note is that since this new package is samba specific, if you're interested in NFS ( which was an option in the former method ) you're out of luck.