One of the arguments used against purchasing anything but Windows-based computers for students is that they should learn how to use the tools that run the business world. I consider this a completely specious argument; students should learn about computing in general, not Window specifically. For most school-age students, the software they're using today will decidedly not be current when they reach the workforce.
In an article about the XO Computer, an inexpensive third-world laptop, Nicholas Negroponte addresses a similar concern about teaching Microsoft Office, but does it so much more eloquently than I:
"In fact, one of the saddest but most common conditions in elementary school computer labs (when they exist in the developing world), is the children are being trained to use Word, Excel and PowerPoint," Negroponte wrote in an e-mail interview. "I consider that criminal, because children should be making things, communicating, exploring, sharing."
I would extend the observation to world-wide, not just developing countries. Students need to learn how to write, how to give presentations, and how to logically process numbers in tabular arrangement. That's not the same as "using Word, PowerPoint, and Excel," which are but single tools to achieve the broader goals.