I have 2 iMacs at home and wanted to cross mount /Users home directories to each other so my family can log into either and have their environment.
Using dscl and automount it's easy.
Good pointers for automount/autofs and dscl (not really good but better than nothing) help.
On the machine that you want to automount directories on, execute:
dscl -change Local/Default/Users/kate NFSHomeDirectory /Users/kate /home/kate
dscl will change the home directory of kate from the normal /Users/kate to /home/kate. This step readies for the use of the automounter.
Edit /etc/auto_home to look like:
#
# Automounter map for /home
#
+auto_home # Use directory service
kate dining-room.local:/Users/kate
This snippit will automagically mount the home directory on the dining-room machine onto the local /home/kate directory (it uses bonjour for host resolution and nfs for mounting).
After a bit of time ... poof the directory will be there when kate logs in locally (already created a local account for kate).