I spent the evening coding, last night -- about 3 hours. I've done some of the battery tweaks recommended on these forums, but I was also VPNed into the office that whole time, too, so wifi was continuously active. I checked the battery before closing up shop and it was at 62% with 3:19 hours left. The math comes to around 6 hours, if you just add, but I don't think Windows does a good estimation if you don't use standard power settings. Considering I hadn't had it plugged in all day at work (minimal use, but not none), my guess is that I'd have gotten 7+ hours of continual use. I'm pretty happy with that, for a device that can do pretty much everything I want it to -- and do it well.
After a couple days of experimenting, I stopped bothering to take my power cord to the office with me. The odds of me actually running out of juice are absurdly low. The Android phone I used to have had worse battery life than the Surface Pro.