We've flown many times with Virgin and, to be honest, I can count on one finger

the amount of times we've taken off on time. However, by far the norm we always seem to make up the hour or so, so if the delay is only an hour(ish) it usually is made up.
Some delays are caused by "technical problems" - ie the ground crew engineers checking things out - I personally feel happier they are doing this than letting the plane turn around with a potential problem.
Sometimes there is a medical emergency which means the plane has to either turn around or stop somewhere enroute. Frustrating, but imagine it was someone in your family (or even yourself) who had a potentially life-threatening problem. This has a knock-on effect for the other leg of the flgiht's return journey. We've had this a couple of times with diabetics who have not taken their medication/low on sugar (now you would think they would ensure they did this given a 9 hour flight

).
I too am sad and check the arrival/departure times on teletext - my poor DH thinks I'm really weird
It's when they use the old "the plane was late in" excuse - and it wasn't - that gets me. We had it going out to San Fransisco this Easter. We stayed up at a Heathrow hotel the night before and, like where we've stayed at Gatwick, they have the 'Saddo Channel' devoted to arrivals and departures. I checked these and knew that the incoming flight had actually arrived half an hour early - so why use the excuse that it was late coming in for the delay

. Luckily for VA

, they made up the time en route.
Like others have said, a small delay like that is nothing - think of the times you've queued for a ride for this amount of time. However, I too find it incredibly frustrating - it makes me stressy

too.