If you do a speed report on Plone.org you notice that the three biggest files it services are
index.html. If you run these through my little slimmer whitespace optimizing program in Python you get the following results:
Using an on-the-fly whitespace optimizer isn't always the right thing to do but in the case of this particular site you prevent serving: 26Kb in 0.1 seconds (on this computer).
26Kb isn't a lot by looking at their traffic summary you see that they could serve 3.3Gb less per month (before gzip compression). That's a big save.