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Would an iPad with the wireless keyboard be an option. If you aren't doing a lot of excel work the iPad may be a good option for you with the keyboard and a lot cheaper as well. I did an entire year of using my ipad2 this past school year and typed notes on it during class and it did wonderfully.
 
There are lots of solid 15" Wintel notebooks for much less than the MBP equivalent. Samsung makes some really good alternatives. Your wife sounds like she really has no preference on OS. She just wants a machine with a bigger screen. I guess I'm lucky that I live close to a Microsoft Store. I bought a laptop there and I've been able to get anything wrong with my laptop fixed as fast as at an Apple store.
 
Bear in mind that when looking at these cheap windows 15" laptops, most of them seem to have a resolution of 1366X768, compared with the MacBook Pro's 13" at 1280x800, or 15" 1440x900 and you can see that while you may be getting a physically bigger screen, it gives you the same screen space as the 13" MBP
 
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