In the cities, where they are playing 2 shows, they stay overnight for sure (Milan, Paris, Amsterdam, Gotheburg, as LU said). And they stayed in Berlin. In Gelsenkirchen helicopters were waiting for them after the show (but don't know where they were going). I missed them in Amsterdam, but nevermind.
@lauramullen- I heard they left Dublin for Nice right after the 3rd show. (But as I haven't seen them at the airport personally, I've no idea if the rumors are true. But people saw their airplane on Dublin airport outside the hangar on the Monday of the 3rd show.)
EDIT:
Independent.ie
U2: Access all areas
This is a reference to the fact that Bono's kids will join him and Ali
in France for the summer, for the first part of the tour, fitting in
with school holidays.