"Sugar is free software, and contributing to it is a good thing to do. But don't forget the goal: helpful contributions are those that make Sugar better on free operating systems. Porting to Windows is permitted by the license, but it isn't a good thing to do."You can read the rest of the essay titled "Can we rescue OLPC from Windows?" here.
P.S. Don't you just love the fact that R.M.S. migrated to the XO because it's the only machine which really fulfills his requirements in terms of only running free software (if you disable the WLAN chip that is)?