I've seen data on student suggesting that 90% of the laptops on certain campuses are OSX, a complete inversion from 10 years ago. This was coupled with an increase in computer ownership by students moving up to 100%.
If we include iPhones however...
http://itc.virginia.edu/students/inventory/compare/
While laptop ownership is near universal; the OS distribution is trending strongly towards OSX but with only about 45% in 2009.