I've had my Surface Pro 3 now for two months and I wanted to give my insights on how its working out.
First off, I'm still amazed at how portable it is, basically I'm carrying around a tablet instead of a laptop. The battery life is such that I can avoid including the charger and cable. Something I feel less inclined to do with my laptop.
The type cover works well for lap type uses, but I'm left wanting when using it on a desk, more specifically the touch pad. I've never been a fan of a touchpad and the type cover's touch pad is worse then my RMB. Including a portable mouse is probably the best answer to that issue, though I've been using the pen on those situations.
Performance is decent, but its along the lines of the MBA, where as my rMBP even at 2.5 years older, is faster. I see it plowing through my images in Lightroom no problem at all, where as the SP3 bogs down quite noticeably. Not a huge issue, as my use of the SP3 is mostly office apps and work with some LR work. Office for Windows is much much better then Office for Mac, but that's a conversation for a different thread
Windows - Very stable, 8.1 so far seems to be the best version of windows, though I'm looking forward to win10. Still, there are niggling little issues that are windows only. A reboot quite often fixes that, though I tend not to need to reboot my rMBP. antivirus issues also have been bugging me. I mean my Antivirus app was corrupting attachments. In contacting the vendor (Avast), they had me repair the install - we'll see if that corrects it.
As a daily driver, I'd say its serviceable, though for me, I'll use my rMBP. For tasks that best suit the SP3, then that will be what I choose. I'll probably be traveling in March or April and I'll be using my SP3.
I suppose since its now my travel machine, I could sell my rMBP and get an iMac but that would be a different discussion