There is one European habit I wouldn't mind Americans adopting: The rhythmic applause used to show huge appreciation and/or demand an encore.
The audience starts out with the usual applause: hundreds if not thousands of hands all clapping, according to each pair of hands' owner. And then, as if someone throws a switch, in one beat the applause is in unison, hands now clapping a regular beat together, firmly, loudly. This performance by the audience is just as fascinating as what was performed on the stage.
In Norwegian, this type of concerted clapping is called "trampeklapp" - "stamping clapping". And yes, the concert was great and we got our encore.