Ubuntu.com was unavailable for some short periods during yesterday's release of Ubuntu 9.10 "Karmic Koala":
The 9.10 versions of Kubuntu, Xubuntu, Edubuntu, Mythbuntu, and Ubuntu Studio were also released at the same time.
The Ubuntu.com website is itself powered by an Ubuntu server running Apache 2.2.8. Netcraft's October Web Server Survey found a total of 1.4 million websites being served from known Ubuntu machines, nearly all of which were running the open source Apache web server.