Removing unnecessary foreign languages. The freeware [Только зарегистрированные пользователи могут видеть ссылки. Зарегистрироваться...]
lets you do just that.
There are many foreign language resources that are installed by default when you install Mac OS X, though if you custom install, you can prevent them from being installed.
If you didn't realize you installed foreign languages to begin with, or want to remove what was installed, the freeware will help you make up for lost time.
This will save you as much as 200 MB to 600 MB of disk space, thus giving the system more room to breath.