Not sure why people are always comparing the MBA with the SP3 as they are nothing alike. SP3 is a hybrid, MBA is a laptop, SP3 has an active digitizer and can act as an electronic notepad, the MBA does not and cannot.
Er, because that was
literally Microsoft's entire SP3 marketing campaign. When it comes to laptops, there is not really much that can compete with an MBA in terms of design, portability and especially battery life. In fact there was a report not long ago that compared the endless plastic dregs that most windows OEMs drag out, and concluded a MacBook Pro was a much better choice of PC on which to run windows. So in Microsoft's, and many others eyes, if you want to be the best you have to first beat the best.
To the OP, I know many have gone from Mac to SP3, and I guess it depends what you need out of it. You said you've only had the mac for a couple of months, so are you normally a Mac user or Windows guy?
As above, both machines are more than capable of what you've said. The tablet part of the SP3 will certainly be better for watching movies, but I'm not sure how the Type Cover will compare to the real keyboard base of the MBA.