So many mis informed or flat out ignorant comments on here
I don't want to take the time to adress them all, but I will say the Surface 3 is an amazing product and competively priced. People are quick to point out the added cost of the $130 keyboard but fail to mention all the short comings of the MacBook air. Do yourself a favor and take a more objective approach to really find out how the two stack up both in features and in price. Only then can you make an informed decision on which one suits your needs best. Keep in mind everyone's needs are different.
MacBook air 11in. $899
i5 1.4ghz
4gb ram
128gb storage
11.inch non hd screen 1366 by 768 (non touch screen)
One 720p camera
Height: 0.11-0.68 inch
Width: 11.8 inches
Depth: 7.56 inches
Weight: 2.38 pounds
Comes with keyboard
1 extra USB port
Surface Pro 3 $999
i5 1.9ghz
4gb ram
128gb storage
Height:.36 in
Width: 11.5in.
Depth:7.93in.
Weight: 1.76 lbs
Trade off for keyboard:
12 inch screen 2160 x 1440(10 point touch) vs non hd non touch
Active digitizer pen input
Gyroscope
Accelerometer
Magnetometer
Ambient light sensor
2 5mp camera(front and rear) vs 1 720p(front)
SD card reader vs (only available in 13in. MBA or higher)
$129 for optional removable keyboard
With the keyboard included in the Surface Pro 3 you're looking at a $229 price difference, but for that you're getting so much more in return. A bigger, better, multitouch HD screen, active digitizer pen support, gyroscope, accelerometer, magnetometer, ambient light sensor, 2 5mp cameras vs 1 720p, and a SD card reader.
The surface pro 3 is also lighter and thinner making it more portable and has the added flexibility of being a tablet/ultrabook. While the surface pro 3 has improved on its ability to be used on the lap its still not as sturdy as the MBA. Outside of your personal preference for OS that's really the only strong point the MBA has over the SP3. Of course this comes down to wether the extra features and portability of the SP3 is worth the price difference. I'd argue, that for many, the screen quality and pen support alone is.
Looks like Microsoft is also using a newer, higher clocked CPU from Intel adding even more value to the SP3.
http://www.anandtech.com/show/8037/microsoft-surface-pro-3-hands-on-display-performance-preview
The model they're using is the 256gb, but the CPU is the same on both the 128gb and 256gb models.