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I, personally, create separate partitions for /(root)(5gig), /boot(50Mb), /usr (4gig) and /home (the rest). I have quite a few other partitions too, but this is my minimum.
Why, because if I need to re-install for any reason, I don't have to format /home.
Generally the installer will want to format /(root) and /usr, at least.
Keep in mind that /var/www, /var/ftp, /usr/local and /opt may also be on separate partitions.
/usr/local for kde3 apps (on a kde4 sys) and some source installs are saved here.
/opt, virtualbox is installed here.
/var/www, apache web files here,
/var/ftp, source files from install may be found here, "copy to disk"
Hope this helps, Regards and welcome to LQ! Glenn