I just have tried smbnetfs with ubuntu 11.4.
I set up a test samba share using nautilus file manager and put /etc/samba/smb.conf, /etc/smbnetfs.conf to ~/.smb/ directory along with smbnetfs.auth.
So when I copy files through smbnetfs share (from localhost to localhost) the transfer speed is ~200kb/s. If I use the network manager of nautilus (gvfs) it is ~25mb/s.
Has anyone an idea of what is wrong?