First, I have to give credit to Rajeev Karamchedu's blog entry for getting me up and running on autofs (specifically the stuff in part 2). Apple did a great job advertising this feature and a terrible one telling you how to work it.

If you're getting either of these errors in your /var/log/system.log:
/usr/sbin/automountd[18521]: map /etc/auto_smb: line too long (max 4095 chars)
/usr/sbin/automount[18533]: map /etc/auto_master: line too long (max 4095 chars)


The problem is you didn't end your file with a newline. Just add a BLANK line to the end of either auto_smb or auto_master or whatever other auto_* file you're using and the error should disappear.

Additional Note:
Do not do the following line to make your mounts appear as directories inside of your home folder:
/Users/adam/mounts auto_smb

This will cause your home folder to instantly (after automount -vc) disappear and be replaced by your blank automount folder. Fortunately, once you remove the line and restart your computer it'll be back to normal.