As a foreigner living here, I try to accept the noise as part of the culture, even though the noise annoys me. So it is great to read of locals actively campaigning to reduce noise levels.
On Friday I was in the very plaça (Plaça del Sol) mentioned in the article with a friend, and it was crowded and loud. All the tables were full, people were sitting on the steps, and indeed all over the plaça. My friend said, "it must be bad for the residents". It is good to know at least one plaça in Barcelona is now moving the crowds on after 11:30pm.