I had the pleasure of T5 back in May, not in the conventional sence however. I had been for a weekend visit to Chicago from Heathrow T4 and only realised upon checking in that our return flight was landing in Gatwick while our car was stuck at Heathrow T4/5 Parking... Not good since I was supposed to be at work within 4 hours of landing!
So on landing in Gatwick we got the national express coach to Heathrow T5. The building itself was very nice and open, not like the busy T3 or Gatwick South, but I guess on hindsight this is because no one wants to fly from it!
Back to my point, after leaving the coach all we knew is that we had to get to stop 50something for our airport parking shuttle and stepping into T5 there was NO airport staff to ask for directions, NO maps and NO signage to point us in the correct direction. I tried asking the person on the Costa coffee counter but they were Polish and didn't understand much English other than Grande Latte (Notice the irony?). In the end I was helped by a nice BA check in counter lady after wasting 10 minutes looking for BAA employees.
In short; nice building, useless staff if you can even find them.