Maybe if your trip is short but definitely not for long term use.
Depends.
I bring my iPad and Apple wireless keyboard on trips. It works great and is a lot lighter than my MBP. For email, general stuff, it's great.
But it's not supposed to be a full-blown replacement for a laptop of desktop. It's decent for traveling and I recently read a story about a professional blogger/writer who ditched his other computers for a year only using his iPad and a wireless keyboard. It can be done.
For an entire 36 weeks . . . I would probably go with the MB Air or the MBP Retina (it's only about 1.5 lbs heavier).
And as others have said, just Bootcamp or VMWare it for Windows.