I don't believe that they've done anything that any installation wouldn't have do to scale beyond a single server. It is documented somewhere (try a search on "load balancer"). Acquia has done something similar and there is documentation on that somewhere too.

Nancy

Injustice anywhere is a threat to justice everywhere. -- Dr. Martin L. King, Jr.

From: Gregg Marshall

And I vaguely remember reading somewhere that Drupal.org is not a stock
Drupal installation but has been modified to aid its performance.