There is an easy way to free about 10% of the used disk space under /usr.
Most (all?) packages in Debian ship with translations for a large number of
languages. On a personal computer with only one or a couple of users there's
usually only need for a single language, so why not delete all the unneeded
translations to free up some space on /usr?
Install the localepurge packet,
select which languages you want to keep, and localepurge will
automatically remove all other translations every time you install or
upgrade a package.
As localepurge does not remove existing translations after the installation, you need to run
$ localepurge
manually as root.
Note: localepurge has worked fine for me on several machines, but
not everyone has been as lucky.
For more information on internationalisation (i18n for short) and localisation in Debian, visit the homepage of the Debian i18n Task Force.