One thing that can be guaranteed is that T5 wont be running smoothly in a few days. I'd suggest months and BA seem to be indicating they think similar too with the possible postponing of moving T4 flights to T5.
What surprises me is so many seemed surprised given the track records of BAA and BA in recent years. My travel plans until September were made in order to avoid the new terminal. Regrettably the top management of BA and BAA reflect that of many a company these days. Over reliant on too few further down the food chain, getting away with it most of the time and then one day it breaks.