When you share a directory from OSX Mountain Lion via SAMBA you can mount it from Linux but you cannot write into it.
This problem is related to a new authentication mode present into Mountain Lion (and also in Lion). To resolve this annoying problem, you have to add this parameter to the mount command: nounix,sec=ntlmssp.
sudo mount.cifs //SERVER_NAME/SHARE_NAME/ /home/LINUX_USERNAME/mnt/ -o username=SMB_USERNAME,rw,uid=LINUX_USERNAME,gid=LINUX_GROUPNAME,ip=SMB_SERVER_IP,noperm,nounix,sec=ntlmssp
SERVER_NAME = you Mountain Lion machine name
SHARE_NAME = you Mountain Lion SAMBA sharing name
LINUX_USERNAME = your Linux username
SMB_USERNAME = your Mountain Lion username with SAMBA permissions
LINUX_GROUPNAME = your Linux group
SMB_SERVER_IP = you Mountain Lion IP address