I wish I could give you a detailed answer, but so far I've only used it to complete a couple projects on the road that I'd started on my iMac at home (Creative Cloud makes that easy).
My initial impressions:
It's not perfect. Photoshop isn't really designed for touch. The tools and menus appear very small on the screen, so I needed to use the stylus, not my finger, to select them. That's just a minor inconvenience (it'd be nice to be able to use my left hand to select tools when I'm in a hurry). You can pinch and zoom artwork, and rotate it (although I ended up just rotating the whole tablet most of the time like a real sketchbook, it was faster).
It's tough to use the quick key shortcuts with the on-screen keyboard, so I used the Surface Pro 3's keyboard cover (sold separately) and the experience was the same as using a desktop. But that defeated the point, I couldn't just kick back, hold it like a tablet and draw. If it hadn't gotten such lousy reviews re: quality control, longevity and customer service, I'd have opted for Wacom's Cintiq Companion over the Surface Pro 3 largely because it has buttons I could've programmed to replace the most common shortcuts I use.
The Surface Pro also lags behind the Cintiq on pressure sensitivity, but Photoshop brush settings, and/or working at a slightly higher resolution, compensated well enough for that. At the end, I couldn't tell the difference between something I'd drawn on my iMac and the work I'd done on the Surface Pro 3. The Surface Pro would not be my choice for a primary Photoshop system just because of the keyboard shortcut issue. But it's great for finishing jobs on the road, sketching, or beginning jobs that I'll later refine on the iMac. It does work ok for completing a project from start to finish, it just takes a little extra time, especially if you use the on-screen keyboard.
On the other hand, that's probably something that improves with practice. It works great with programs designed with touch in mind, like Manga Studio. And the portability is life-changing.