Wikipedia is ditching out a mix of Red Hat and Fedora for Ubuntu Linux. Wikipedia has 10 million articles in 250 languages and it is one of the 10 most visited websites in the world.
One of the reasons for this switch was that they did not want to pay Red Hat for support on their provided software solutions. Ubuntu Linux get updated frequently and nothing can beat apt package manger.
According to Vibber, CTO of the Wikimedia Foundation:
We had a mix of things: some Red Hat 9, some Fedora -- several different versions. The group used a custom-scripted installation procedure, but found that having a multitude of versions was more difficult to maintain for its small five-person IT staff around the world. The move to all-Ubuntu was primarily done with the goal of "making our own administration and maintenance simpler. We decided that we want to standardize on something.