[Alupis]

> Mine is far from the largest Drupal site, so other sites like Weather.com and The Onion have done more with large-scale scaling in terms of multiple servers and the like

Don't forget https://www.whitehouse.gov - it's a Drupal 7 site, and I imagine it gets a fair amount of traffic.

[JohnTHaller]

The traffic estimation sites online peg whitehouse.gov at around 3m monthly visitors as well.