I refer to this (Angus Kidman, CIO Online) article about how a New Zealand high school has completely switched to open-source software, despite a national contract with Microsoft regarding computers for education.
This is a great move, not least because of the great software involved: Ubuntu for the front-end, Mandriva for the servers, and OpenOffice.org and Google Docs for productivity, among others. The biggest benefit has been...wait for it...
a reduction of server requirements by a factor of 50 (!) for its main servers (now it only uses 4 main servers).
The other thing the administrators were happy about was the openness of it all: no longer did the school have to pay full fees for separate limited licenses for specialized Microsoft software, and the source code for those programs is now freely available to all schools for viewing, distribution, and modification.
I think this is a model that could work for all schools; the only thing hindering this sort of thing for MCPS would be the Promethean board program, whose boards would need to somehow be reengineered with software rereleased for Linux compatibility. Other than that, it could definitely work. And for those that say that kids today would be unprepared for a Windows world, that Windows world may no longer be a Windows world when the employers see all the kids coming out of school trained on Linux.