I found out what I was doing wrong, when I couldn't browse Ubuntu shares from
Windows. Alas, just because you can print from a Windows box doesn't necessarily
mean you have Samba installed. Do it!

The default smb.conf was okay for my purposes, once the lines were uncommented
to create home shares. Otherwise you don't have any shares.

Finally, the password you chose when you installed Ubuntu won't get you into
Samba. Use sudo smbpasswd -a username to do this.