Seat Belts: I think there is an issue here too, but might best be discussed in the cabin crew forum
White smoke: Could well be 150 tons of Boeing chewing up the concrete.
To the Pilots, from an Avionics guy: I would rather be in the back, with an average pilot that is a little wary of the avionics, than a great pilot that put 100% trust in them. (I know great ones don't) These systems have become so interconnected that a fault in one system can introduce a fault in an unrelated system.