For those who still have to go :
we left at 4:30, and arrived at 8.
Muse started to play around that time, U2 started around 9:30. People were coming into the stadion till that time! Parking spaces are hard to find.
We left the stadion just after 'with or without you' (they did at least 1 other song after that), and the streets (between the stadion and the highway, 4km??) were full, really full of cars, taxi, remis, combi, busses waiting. Driving back took us 30 minutes. I can't imagine how long it would have taken us if we had been in the middle of traffic... I imagine it must have been complete chaos.
If you are driving, get yourself a little map, it easy when you are looking for a place to park.
BTW, the concert was absolutely great...