I just had the dubious good fortune of using three different terminals at Heathrow in the space of a few hours (arrival at 3, over to 4 for the arrivals lounge, and departure from 1).
I have to say that apart from the obvious exceptions, such as private lounges, the entire airport is without exception a complete disgrace. It makes me cringe to think of the first impression of the UK given to arriving visitors from around the world.
My general plan is to check-in either on-line or at Paddington, spend any time I have at LHR on the spectators terrace (even in the rain if necessary!) and only enter the terminals at the last possible minute.
Perhaps the demolition workers currently at Wembly should turn their hands to Heathrow when they've finished up there.
Will T5 be any better? Not holding my breath.