If you do a speed report on Plone.org you notice that the three biggest files it services are plone.css, plone_javascripts.js and index.html. If you run these through my little slimmer whitespace optimizing program in Python you get the following results:

 $ python slimmer.py --test http://plone.org/plone.css
 Took 0.016 seconds
 Bytes before: 29355
 Bytes after:  20265
 Bytes saved:  9090  (69.0% of original size)

 $ python slimmer.py --test http://plone.org/plone_javascripts.js
 Took 0.057 seconds
 Bytes before: 27251
 Bytes after:  19974
 Bytes saved:  7277  (73.0% of original size)

 $ python slimmer.py --test http://plone.org/ 
 Took 0.029 seconds
 Bytes before: 37186
 Bytes after:  26466
 Bytes saved:  10720 (10K)  (71.0% of original size)