I'm working on a report for CoSN.org right now on large-scale Linux deployments. This comes from an all-day international meeting I facilitated at the K-12 Open Minds Conference in Indiana on this same topic.
The general thesis is that Linux is uniquely suited to provide inexpensive and ubiquitous computing on a large scale. I'm looking for any and all feedback and examples. Please respond here or email me directly at steve@hargadon.com.
Please define "Large" scale... All of our servers in our District are Linux (ie. mail, LTSP, file, web) The only ones that have remained Windows are the ones specific to the specialized application. However, we have been testing with virtual machines. So far, the apps have worked flawlessly running on an instance of Windows loaded on a Linux server. We are converting all of our phone systems to Asterisk (Linux VoIP).