Well, the big reviews at Engadget and The Verge are up.
The consensus is fairly similar: they both like the Surface Pro 3 overall, but they believe that it's still making a pitch to a fairly specific audience. You have to really like the concept of having one device that replaces both your tablet and laptop (or a pen-driven device) for this to make sense. If you already have two devices, or you want something that's the best in either laptop or tablet tasks, you should probably look elsewhere.
That jives with my experience... it's really cool to have a laptop-like machine that you can use like a tablet, but it's clear that Microsoft had to make some compromises for that to happen. I know I wouldn't want to hold the Pro 3 for very long while standing, for example... it's hefty.
Get to the gym. It weighs less than my Surface Pro and it's not heavy to me at all.