I had a 17" laptop (Dell 9300). I used it in the lounges without problems. Some watched a little bit surprised me unpacking such a monster, but as it's getting more common I don't think many will stare at you. In long haul flight flights in Business I had no problems using this thing, but in smaller planes like A319/320/321 I had no chance using the laptop. The seat pitch is just too small.
As I often travel in Europe where small planes are used I switched to a standard 15" laptop, which is more then enough and allows work in small spaces. Additionally the battery running time is much longer, as the screen is a huge power consumer. And the whole handling is easier.

Just my 0.02$
W