How to set OS X Terminal's default home?

This is a bit of under-the-hood fiddling, but you could simply enter

cd <directory>

in /Users/<yourUserName>/.profile

and startup a new terminal. You should then be in the directory you want.

You probably want these instructions for how to use the command line:

https://superuser.com/questions/154193/setting-a-users-home-directory-on-mac-os-x-server-from-the-command-line

Basically, use the dscl command line tool to see what the system thinks your home directory is set to, or to try and reset it....