With a source-based distribution, each software is tied in one single
    package, I mean the source, that you can customize according to your
    needs with the USE flags (I am thinking about portage, a package
    management system)

Sorry, I don't understand any of that in concrete terms.

--
Dr Richard Stallman
President, Free Software Foundation
51 Franklin St
Boston MA 02110
USA
www.fsf.org  www.gnu.org
Skype: No way! That's nonfree (freedom-denying) software.
  Use free telephony http://directory.fsf.org/category/tel/