The failure of Vienna, Austria's open source migration program teaches a powerful lesson to enterprises of all sorts. (Jon Voight played Milo Minderbinder in the film version of Catch-22.)
Open source migration should not be a religion. It needs to be a practical step, actually a series of practical steps, each taken for practical reasons.
Wholesale migration is very, very tough to pull off. I know of someone doing that with an application stack and it's taken years-and-years. Systems are just too complex to allow that kind of wholesale rip-and-replace without very careful planning.
That lack of planning seems to have plagued Vienna. That, and a lack of testing. Maybe some Microsoft sabotage. Whatever, the problems spooked the constables into switching all the way back, at immense cost.
The right way to do an open source migration is slowly, step by step, application by application, bit by bit. That is generally how the world is moving, with open source slowly increasing its market share.
The wrong way to do an open source migration is all at once. And the way you go down that road is by selling it as religion, or politics. It's not. It's business.
Think of open source as evolution in action.