I would like to put some additional information in here. There are many ways to share files.
Number one is OS. Linux sharing is much better with NFS. NFS offers better utilization of
bandwidth and with with V4 better security.
With Mac I would consider Netatalk. Netatalk is the open source version of AppleTalk. It
makes your network Apple friendly by integrating with Mac OS and looking like a Mac server.
I agree CIFS (Samba) is the universal file sharing program but there are a lot of down sides.
CIFS is much slower than other alternatives. Also in my experience Mac and Linux support has
many bugs because no one computer is the same nor every windows installation so its hard to
provide compatibility across everything.