Munich and Bergen (second largest Norwegian city) already decided to do it. It is important to note that the highest part of the switching costs for the whole migration thing is the personnel training. And most difficult of course since it involves people changing. Some friends of mine working in the software industry also recently switched to Linux (company's policy - Windows is too expensive) and even though they're software programmers they waste a lot of time trying to learn and adjust.

UPDATE: The Wimbledon tennis tournament will have its technology infrastructure run on Linux too.