Here in Barcelona we seemed to reach a peak around last year, when they seemed almost constant. They're still pretty common now, but I get the sense security cracked down a bit and handed out some real fines.
I don't mind a guitar or violin here and there, but a lot are singers and rappers who wheel around big, pounding speakers. It can be pretty bothersome if you're coming home after a long day or going to take an exam when a guy shows up to blast salsa music and do his little singing over it.