One of my key concerns is not the time in the air but the time on the ground. I can be sure that flight crew have a whole lot more info than they had six months ago - but the ground crew?
Are ground crew at small outstations (not normally expecting to ever see the 787) ready? OK, the a/c is not going to be towed long distances, or at all, on such SH ops. Also the fire crews, in Boston they had been given no information about the nature of the battery they were dealing with! These items are all in the cheese. There are other reasons why I prefer to sit this one out for a while.
I agree with Hartington about early big twins and ETOPS. In fact, I can guess that I will never feel comfortable about it - eventhough I will increasinly have little choice. But that is my generation.
I am well aware that all carriers can substitute the equipment at any time and if I refuse to board that will be my financial risk. In the early days, one might hope that Thomson and other carriers would prefer to let me quietly board another flight and not have a public row about it. They have, of course, to get back to where Boeing promised them they would be, before Boeing made such a Horlicks of the production process, leave alone the battery.
Another example. When the A340 started, I waited a bit and was not happy about the A346 until they had sorted the balancing act. The last time I was on one, it still had a small - but obvious - roll for the duration of the cruise.