Last night I was on ORD-SFO and it was the new 777 with 3-4-3 in the back. The seats were, believe it or not, more comfortable to me than the slimline seats on the A319/320 as more of my thigh was supported.

Pro's:
* Better leg support which makes sitting more comfortable
* No dreaded middle-middle-middle seat, doesn't feel as cramped
* "Media holders" for cell phone and tablets in the seatback in front of you; you no longer need to hold your personal device entertainment and your tray table is completely free to be used for food, laptop, or papers ... etc.

Con's:
* The overhead light and FA call button are on the arm rest RIGHT WHERE YOUR ELBOW will be if you use it as an armrest and not just a seat divider. The "ding" for the FA call button will go off continuously for the duration of the flight, about every 3-10 seconds ... even after the Purser made an announcement about it.
* The two middle seats in the "4" section have seat row supports right where your bag would go if you're to place it under the seat in front of you. This means seat E & F will share a space which makes it awkward. Not sure about the middle seat in the "3" sections.
* The aisles feel really tight in Y, giving the FAs not much room to avoid hitting elbows, seats, and knees.
* The recline of the seats in Y don't really feel like they recline much. The seat bottom does slide a bit forward, but I like more of a recline angle.

Wish I took some pictures to share :-(

YMMV.