I too have been a "trial passenger" at T5. I quite like the building. At the moment you get a great feeling of space. But I have my reservations. Many of the trial passengers don't seem to be regular travellers (nothing wrong with that as such), The result is an element of the herd instinct (just follow the person in front) which has some relevance for arriving passengers but not for departing. I'm also doubtful how much thought they are putting into their questionnaire answers.
The result is that I think there are a lot of shining reviews which may be leading BA and the BAA into a false sense of security. In particular I think there are some missing signs. For instance, acting as a transit passenger I found my way from T5B to the connections centre in T5a (using the TTS) and went back upstairs to be rescreened. But on exiting screening the gate wasn't promulgated and there was no indication what to do/where to go which resulted in people milling around immediately after security. Then as an arriving passsnger I got into the baggage hall and thought "where is the exit?" I'd missed a small illuminated overhead sign (which wasn't illuminated) at the foot of the escalator. There was no other sign pointing to the exit and when I questioned one of the hosts I was shown the (non) illuminated sign and told that the design of the wall in which the exit is situated called for it to be flat with no protruding signs which meant they couldn't put one up to point at the exit!
Anyway I'm taking the plunge and using it for real on 1st April so wish me luck. At least I now know where I'm likely to have to go.