filelight: how to clean up unnecessary files to get more free space (linux, gentoo)

Ever had the problem, that harddisk on your linux machine has just filled up and you couldn't find out what files took so much space? The Czech magazine linuxexpres wrote about a great tool to determine the folders that take up most space. It's called filelight and it analyzes the size of all the files on the harddisk and draws a picture consiting of rings that helps you reveal nests of unneeded temporary files or overgrown backups...

My disk before cleanup:
unnecessary files that just take up space (created during compilation of openoffice from source and other temporary files):

disk after cleanup:
enough space for my home folder and necessary files :))