It's not currently a default feature, but since MySQL 5.5.10 you can easily enable UNIX socket authentication.
Add the following to your MySQL config file:
[mysqld] plugin-load=auth_socket=auth_socket.so
Restart MySQL, then you'll be able to use IDENTIFIED WITH auth_socket as a replacement for IDENTIFIED BY 'password'.
Makes things easier for local installations for services running under a specific account, or for limiting access to the root account to the local root user.